'Utilizando las APIS, esta es una de las formas de obtener el size de un archivo.
Const GENERIC_READ = &H80000000
Const FILE_SHARE_READ = &H1
Const OPEN_EXISTING = 3
Const FILE_TYPE_CHAR = &H2
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, lpSecurityAttributes As Any, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Private Declare Function GetFileSizeEx Lib "kernel32" (ByVal hFile As Long, lpFileSize As Currency) As Boolean
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Sub command1_click()
Dim hFile As Long, nSize As Currency
hFile = CreateFile("c:\SIVI_final.exe", GENERIC_READ, FILE_SHARE_READ, ByVal 0&, OPEN_EXISTING, ByVal 0&, ByVal 0&)
GetFileSizeEx hFile, nSize
CloseHandle hFile
MsgBox "Size:" + Str$(nSize * 10000) + " bytes"
End Sub