On Error Resume Next

Dim oAcad
Set oAcad = GetObject(, "AutoCAD.Application")
If Err Then
    Err.Clear
    Set oAcad = CreateObject("AutoCAD.Application")
End If

Dim WshShell
Set WshShell = WScript.CreateObject("WScript.Shell")

Dim oCmd
Set oCmd = WScript.Arguments

With oAcad
    .Visible = True
    .WindowState = Normal
    .Documents.Open oCmd(0), True
    WshShell.AppActivate(.caption)
End With