Vista Bsness VPN connects but has no access to Intra-Intnet / Resr

I have a SBS 2003 R2 wih ISA Svr 2004 and until last friday my XP Pro laptop
was working fine wih an AT&T (Option GT Max 3.6 Express) for everywhere
access. I had a VPN connection configured and everything was fine. I made an
upgrade to Vista Business and I'm having problems with the VPN connection.
The symptom is: Before connecting to VPN, I do have Internet access, but
after supplying credentials for VPN connections, everything seems fine: the
connection is active and the Firewall Client icon appears connected but I
cannot access my Intranet (companyweb), Internet and Network resources.
I've applied what KB articles 930163 and 929853 state. I've tried updating
the software and driver of the Option GT card and everything has been
unsuccessful.

The problem seems not to be in the Option GT card because I have the same
results when I use the Ethernet NIC for Internet connection.

Does anybody know about a solution for this problem?

I'll really appreciate if someone provides a solution, I've been working in
this problem for 2 days now.
Thanks