VPN – can’t map to remote machine. Different symptoms.

I’ve checked the following on four different machines (XP/Vista). They all can connect to a VPN (login), but only TWO of them can map to the remote server on the other side.

Here’s the twist, the two that can NOT map a drive…can still ping AND RDP (remote desktop) to that server!

Of course, one of the machines that can not map is a brand new VISTA laptop. GRRRRRRRRR!
Note: “IPconfig /all” shows similar ranges for the different machines when using the VPN/PPP.

Any suggestions? I’ll buy beer.