How to Authenticate Domain user thru VPN

We have several field sales personnel that access server resources by first using a dial-up through AT & T and then going through our VPN. The problem is that when doing this the domain user accounts are not being authenticated by the W2k Domain Controller, rather it is saving cached credentials to the local laptop. Because of this these laptops cannot be managed remotely in either direction. Does anyone know if this is possible and how to set it up?

Thanks,
Rob Bronw
Hubbell Premise Wiring
860-535-5556
rbrown@hubbell-premise.com