やっぱりwshが一番楽でした(;´Д`)
まぁどんな言語でもできるに越したことはないんだけどね

Set FS = CreateObject("Scripting.FileSystemObject")
Set REG = New RegExp
REG.Global = True
REG.Pattern = WScript.ScriptName
Set workDir = FS.GetFolder(REG.Replace(WScript.ScriptFullName, ""))

For Each inFile In workDir.Files
  REG.pattern = "(\d\d\d).+?\.[Tt][Xx][Tt]"
  If REG.Test( inFile.Path ) Then
    Set matches = REG.Execute( inFile.Path )
    number = matches(0).SubMatches(0)
    FS.CopyFile inFile.Path, workDir.path & "\" & number & ".txt", true
  End If
Next

これと同じのを他の言語で書くとどんな感じ？(;´Д`)