Problem with VPN Services and Windows XP Clients

Hiya folks, I've had this problem for a few weeks, I've searched here and on the Apple Discussion boards for a possible fix but no luck so far. The problem only effects windows users when linking to a Leopard Server 10.5.3 and 10.5.4 I haven't tried the earlier versions, my 10.4.11 Server works fine. When the Windows workstation connects to the VPN server it connects but is only able to ping machines on the network it can't connect to any mapped drives or my internal wiki. On the Apple Discussion board I've seen that other people have been having the same problem, here is the link http://discussions.apple.com/thread.jspa?messageID=7473350 Any ideas ? Thanks for your time.