Help With a VPN

Hello,
I have two sites connected by a vpn.
Site A is a Windows 2000 ISA server.
Site B is a Windows 2003 ISA server.
When the VPN is established the clients on site A cannot ping any computers within site B. If a client establishes a personal VPN they can ping or browse without a problem. Could the problem be the routing table at site A. its like the clients will not “jump on the VPN”
Thanks allot for your help.
Dan