Chécate éste ejemplo, lo guardas como html para que lo puedas probar y veas
<html>
<head>
<title> New Document </title>
<SCRIPT LANGUAGE=javascript>
function fn(form,field)
{
var next=0, found=false
var f=form
if(event.keyCode!=13) return;
for(var i=0;i<f.length;i++) {
if(field.name==f.item(i).name){
next=i+1;
found=true
break;
}
}
while(found){
if( f.item(next).disabled==false && f.item(next).type!='hidden'){
f.item(next).focus();
break;
}
else{
if(next<f.length-1)
next=next+1;
else
break;
}
}
}
</SCRIPT>
</head>
<body>
<FORM name=fx>
<TABLE border=0 cellPadding=1 cellSpacing=1 width="75%">
<TR>
<TD><b>Campo 1:</b></TD>
<TD><INPUT id=text1 name=text1 onkeyup=fn(this.form,this)></TD>
</TR>
<TR>
<TD><b>Campo 2:</b></TD>
<TD><INPUT id=text2 name=text2 onkeyup=fn(this.form,this)></TD>
</TR>
<TR>
<TD><b>Campo 3:</b></TD>
<TD><INPUT id=text3 name=text3 onkeyup=fn(this.form,this)></TD>
</TR>
<TR>
<TD><b>Campo 4:</b></TD>
<TD><INPUT disabled id=text4 name=text4 onkeyup=fn(this.form,this) value=Disabled></TD>
</TR>
<TR>
<TD><b>Campo 5:</b></TD>
<TD><INPUT id=text5 name=text5 onkeyup=fn(this.form,this)><SELECT disabled id=select1
name=select2 onkeyup=fn(this)> <OPTION selected>disabled</OPTION>
<OPTION>nitin</OPTION></SELECT></TD>
</TR>
<TR>
<TD><b>Campo 6:</b></TD>
<TD><INPUT id=text6 name=text6 onkeyup=fn(this.form,this)></TD>
</TR>
<TR>
<TD><b>Campo 7:</b></TD>
<TD><SELECT id=select12 name=select1 onkeyup=fn(this.form,this)> <OPTION
selected>value1</OPTION> <OPTION>Value2</OPTION></SELECT></TD>
</TR>
<TR>
<TD><b>Campo 8:</b></TD>
<TD><INPUT id=checkbox1 name=checkbox1 onkeyup=fn(this.form,this) type=checkbox><INPUT disabled id=che2ckbox1 name=checkbox2 onkeyup=fn(this.form,this) type=checkbox>
</TD>
</TR>
<TR>
<TD colspan=2 align="center">
<INPUT name=boton onclick="alert('Fin del formulario');" type=button value=" Fin ">
</TD>
</TR>
</TABLE>
</FORM>
</body>
</html>
