VPN access on my Vista Machines

Our vpn is currently provided via a PIX firewall, we use the cisco VPN Client. Users who are using Windows XP Operating Systems have no trouble at all connecting to the VPN and accessing the Local Network, Vista users however will show that they are connected to the VPN but it is really hit and miss whether they will be able to access network resources. One band-aid that I have come up with is when this problem happens I navigate to the Cisco VNet adapter and plug in the default gateway, sometimes it works but sometimes it doesn’t. I am almost certain that it is a config problem within the PIX, but I really don’t even know where to start looking.