Script to move first 3 characters of filename to the end - vbscript

Question

I have a directory full of files that I need to rename. For each file, I need to take the first three characters of the filename and move them to the end of the filename before the extension.
So 003999999.wav would become 999999003.wav.
The scripting language doesn't really matter. It just needs to work in Windows. This seems like it'd be an easy script using vbscript and I'm currently doing some reading, but figured I'd see if someone already has something like this that would work.
Edit - So I think I've found how to do this, except the part on getting the filename characters. Here's what I have.
Set objFSO = CreateObject("Scripting.FileSystemObject")
Set objFolder = objFSO.GetFolder("C:\Directory")
For Each strFile in objFolder.Files
arrNames = Split(strFile.Name, ".")
If arrNames(1) = "mp3" Then
Set objstart = objFSO.Range(0,3)
Set objend = objFSO.Range(4,17)
strNewName = "C:\Directory\" & objend.Text & objstart.Text & ".mp3"
objFSO.MoveFile strFile.Path, strNewName
End If
Next

Answer 1

Try this script. I used simple string functions to manipulate each filename.
'Rename Files
'============
Dim objFSO, objFolder, strFile, intLength, firstThree, restofName, strNewName
Set objFSO = CreateObject("Scripting.FileSystemObject")
Set objFolder = objFSO.GetFolder("C:\Directory")
For Each strFile in objFolder.Files
'Get files by extension
If objFSO.GetExtensionName(strFile.Name) = "mp3" Then
'Use instr to get the location of the "." and subtract 1 for the "."
intLength = InStr(1,strFile.Name,".",1)-1
'Use the Left function to get the first three characters of the filename
firstThree = Left(strFile.Name,3)
'Use the Mid function to get the rest of the filename subtract 3 for the file extension
restofName = Mid(strFile.Name,4,intLength -3)
strNewName = "C:\Directory\" & restofName & firstThree & ".mp3"
objFSO.MoveFile strFile.Path, strNewName
End If
Next
WScript.Echo "Done!"

Answer 2

Instead of the fictional .Range method, use a regular expression:
>> s1 = "003999999.wav"
>> Set r = New RegExp
>> r.Pattern = "(\d{3})(\d+)(\.wav)"
>> s2 = r.Replace(s1, "$2$1$3")
>> WScript.Echo s2
>>
999999003.wav
to cut three digits (\d{3}), the other digits (d+), and the (escaped) dot followed by the extension (wav) from the input string and re-arange the 3 parts in the .Replace.

Answer 3

Simplified version of JP's solution:
Set fso = CreateObject("Scripting.FileSystemObject")
For Each f In fso.GetFolder("C:\Directory").Files
extension = fso.GetExtensionName(f.Name)
If LCase(extension) = "mp3" Then
basename = fso.GetBaseName(f.Name)
f.Name = Mid(basename, 4) & Left(basename, 3) & "." & extension
End If
Next
In batch you'd do it like this:
#echo off
setlocal EnableDelayedExpansion
for %%f in (C:\Directory\*.mp3) do (
set basename=%%~nf
ren "%%~ff" "!basename:~3!!basename:~0,3!%%~xf"
)
endlocal