PHP - Mostrar segundo combo de acuerdo al primero

Hola de nuevo. Necesito que me ayuden, mandandome un script. El problema se trata de que tengo que seleccionar un municipio de acuerdo al estado. Todo esto mediante combos. Sin utilizar base de datos. Ya que los combos ya existen. Lo que me hace falta, es que me muestre el segundo combo, de acuerdo a la eleccion del primero. Espero me hayan entendido. Ya que es urgente. Por favor. Ayudenme.
Aqui les dejo los combos:

//De acuerdo a la eleccion de este:
Estado
<form name="form1">
<select name="menu1" onChange="mostrar(this.value)">
<option> Selecciona un estado</option>
<option value="yucatan">Yucatan</option>
<option value="quintana roo">Quintana Roo</option>
</select>
</form>

//Me muestre ya sea este:
Poblacion <form name="form2">
<select name="select2" onChange="MM_jumpMenu('parent',this,0)">
<option>Elige tu Población</option>
<option>Abalá</option>
<option>Acanceh</option>
<option>Akil</option>
<option>Baca</option>
<option>Bokobá</option>
<option>Buctzotz</option>
<option>Cacalchén</option>
<option>Calotmul</option>
<option>Cansahcab</option>
<option>Cantamayec</option>
<option>Celestún</option>
<option>Cenotillo</option>
<option>Conkal</option>
<option>Cuncunul</option>
<option> Cuzamá </option>
<option>Chacsinkín</option>
<option>Chankom</option>
<option>Chapab</option>
<option>Chemax</option>
<option>Chicxulub Pueblo</option>
<option>Chichimilá</option>
<option>Chikindzonot</option>
<option>Chocholá</option>
<option>Chumayel</option>
<option>Dzan</option>
<option>Dzemul</option>
<option>Dzidzantún</option>
<option>Dzilam de Bravo</option>
<option>Dzilam González</option>
<option>Dzitás</option>
<option>Dzoncauich</option>
<option>Espita</option>
<option>Halachó</option>
<option>Hocabá</option>
<option>Hoctún</option>
<option>Homún</option>
<option>Huhí</option>
<option>Hunucmá</option>
<option>Ixil</option>
<option>Izamal</option>
<option>Kanasín</option>
<option>Kantunil</option>
<option>Kaua</option>
<option>Kinchil</option>
<option>Kopomá</option>
<option>Mama</option>
<option>Maní</option>
<option>Maxcanú</option>
<option>Mayapán</option>
<option>Mérida</option>
<option>Mocochá</option>
<option>Motul</option>
<option>Muna</option>
<option>Muxupip</option>
<option>Opichén</option>
<option>Oxkutzcab</option>
<option>Panabá</option>
<option>Peto</option>
<option>Progreso</option>
<option>Quintana Roo</option>
<option>Río Lagartos</option>
<option>Sacalum</option>
<option>Samahil</option>
<option>Sanahcat</option>
<option>San Felipe</option>
<option>Santa Elena</option>
<option>Seyé</option>
<option>Sinanché</option>
<option>Sotuta</option>
<option>Sucilá</option>
<option>Sudzal</option>
<option>Suma</option>
<option>Tahdziú</option>
<option>Tahmek</option>
<option>Teabo</option>
<option>Tecoh</option>
<option>Tekal de Venegas</option>
<option>Tekantó</option>
<option>Tekax</option>
<option>Tekit</option>
<option>Tekom</option>
<option>Telchac Pueblo</option>
<option>Telchac Puerto</option>
<option>Temax</option>
<option>Temozón</option>
<option>Tepakán</option>
<option>Tetiz</option>
<option>Teya</option>
<option>Ticul</option>
<option>Timucuy</option>
<option>Tinúm</option>
<option>Tixcacalcupul</option>
<option>Tixkokob</option>
<option>Tixméhuac</option>
<option>Tixpéhual</option>
<option>Tizimín</option>
<option>Tunkás</option>
<option>Tzucacab</option>
<option>Uayma</option>
<option>Ucú</option>
<option>Umán</option>
<option>Valladolid</option>
<option>Xocchel</option>
<option>Yaxcabá</option>
<option>Yaxkukul</option>
<option>Yobaín</option>
</select>
</form>

//O este:
Poblacion: <form name="form3">
<select name="menu1" onChange="MM_jumpMenu('parent',this,0)">
<option>Elige tu Población</option>
<option>Benito Juárez</option>
<option>Cancún</option>
<option>Chetumal</option>
<option>Cozumel</option>
<option>Felipe Carrillo Puerto</option>
<option>Isla Mujeres</option>
<option>José María Morelos</option>
<option>Kantunilkín</option>
<option>Lázaro Cardenas</option>
<option>Othón P. Blanco</option>
<option>Playa del Carmen</option>
<option>Solidaridad</option>
</select>
</form>

Espero me ayuden. Gracias.

//De acuerdo a la eleccion de este:
Estado
Fijate si te sirve
<form name="form1" >
<select name="menu1" id="menu1" onChange="mostrar(this.value)">
<option> Selecciona un estado</option>
<option value="yucatan">Yucatan</option>
<option value="quintana roo">Quintana Roo</option>
</select>
</form>

//Me muestre ya sea este:
Poblacion <form name="form2" id="menu2">
<select name="select1" id="select1" onChange="MM_jumpMenu('parent',this,0)" style="display:none">
<option>Elige tu Población</option>
<option>Abalá</option>
<option>Acanceh</option>
<option>Akil</option>
<option>Baca</option>
<option>Bokobá</option>
<option>Buctzotz</option>
<option>Cacalchén</option>
<option>Calotmul</option>
<option>Cansahcab</option>
<option>Cantamayec</option>
<option>Celestún</option>
<option>Cenotillo</option>
<option>Conkal</option>
<option>Cuncunul</option>
<option> Cuzamá </option>
<option>Chacsinkín</option>
<option>Chankom</option>
<option>Chapab</option>
<option>Chemax</option>
<option>Chicxulub Pueblo</option>
<option>Chichimilá</option>
<option>Chikindzonot</option>
<option>Chocholá</option>
<option>Chumayel</option>
<option>Dzan</option>
<option>Dzemul</option>
<option>Dzidzantún</option>
<option>Dzilam de Bravo</option>
<option>Dzilam González</option>
<option>Dzitás</option>
<option>Dzoncauich</option>
<option>Espita</option>
<option>Halachó</option>
<option>Hocabá</option>
<option>Hoctún</option>
<option>Homún</option>
<option>Huhí</option>
<option>Hunucmá</option>
<option>Ixil</option>
<option>Izamal</option>
<option>Kanasín</option>
<option>Kantunil</option>
<option>Kaua</option>
<option>Kinchil</option>
<option>Kopomá</option>
<option>Mama</option>
<option>Maní</option>
<option>Maxcanú</option>
<option>Mayapán</option>
<option>Mérida</option>
<option>Mocochá</option>
<option>Motul</option>
<option>Muna</option>
<option>Muxupip</option>
<option>Opichén</option>
<option>Oxkutzcab</option>
<option>Panabá</option>
<option>Peto</option>
<option>Progreso</option>
<option>Quintana Roo</option>
<option>Río Lagartos</option>
<option>Sacalum</option>
<option>Samahil</option>
<option>Sanahcat</option>
<option>San Felipe</option>
<option>Santa Elena</option>
<option>Seyé</option>
<option>Sinanché</option>
<option>Sotuta</option>
<option>Sucilá</option>
<option>Sudzal</option>
<option>Suma</option>
<option>Tahdziú</option>
<option>Tahmek</option>
<option>Teabo</option>
<option>Tecoh</option>
<option>Tekal de Venegas</option>
<option>Tekantó</option>
<option>Tekax</option>
<option>Tekit</option>
<option>Tekom</option>
<option>Telchac Pueblo</option>
<option>Telchac Puerto</option>
<option>Temax</option>
<option>Temozón</option>
<option>Tepakán</option>
<option>Tetiz</option>
<option>Teya</option>
<option>Ticul</option>
<option>Timucuy</option>
<option>Tinúm</option>
<option>Tixcacalcupul</option>
<option>Tixkokob</option>
<option>Tixméhuac</option>
<option>Tixpéhual</option>
<option>Tizimín</option>
<option>Tunkás</option>
<option>Tzucacab</option>
<option>Uayma</option>
<option>Ucú</option>
<option>Umán</option>
<option>Valladolid</option>
<option>Xocchel</option>
<option>Yaxcabá</option>
<option>Yaxkukul</option>
<option>Yobaín</option>
</select>
</form>

//O este:
Poblacion: <form name="form3">
<select name="select2" id="select2" onChange="MM_jumpMenu('parent',this,0)" style=" display:none;">
<option>Elige tu Población</option>
<option>Benito Juárez</option>
<option>Cancún</option>
<option>Chetumal</option>
<option>Cozumel</option>
<option>Felipe Carrillo Puerto</option>
<option>Isla Mujeres</option>
<option>José María Morelos</option>
<option>Kantunilkín</option>
<option>Lázaro Cardenas</option>
<option>Othón P. Blanco</option>
<option>Playa del Carmen</option>
<option>Solidaridad</option>
</select>
</form>

<script type="text/javascript">
var select1 = document.getElementById("select1");
var select2 = document.getElementById("select2");
function mostrar(valor){
switch(valor){
case "yucatan":
select1.style.display = "block";
select2.style.display = "none";
break;
case "quintana roo":
select1.style.display = "none";
select2.style.display = "block";
break;
default:
select1.style.display = "none";
select2.style.display = "none";
break;
}
}
</script>

Amigable,

Mira mi respuesta a este mensaje " combo box marcela (28/06/2007)", esta mas abajo.

Espero te sirva!!

juanca