If it is the Desktop you are looking for, you can find it in the registry like Les said. I think it goes like this:
Code:

Dim $Desktop
$Desktop = ReadValue("HKEY_USERS\"+@SID+"\Software\Microsoft\Windows\Currentversion\Explorer\Shell Folders","Desktop")
$Desktop

Looking up some information about "Shell Folders", I found this article: Windows Confidential: The Sad Story of the Shell Folders Key. ALso very interesting...