VPN doesn’t support Internet browsing

Currently, we have a number of field users with Windows 9x laptops connecting via dialup-VPN connections, with Cisco VPN client 3.x installed on each laptop.
Recently, we have received several Windows 2000 laptops, and although W2K has built-in VPNability, for purposes of continuity the Cisco client has been installed.
However, once connected via VPN, the user is unable to browse the Internet; if a specific address is entered a site can be reached, but names won’t be recognized.
This would seem to indicate a problem with the DNS, but if that was the case, wouldn’t it affect all users?
Windows 9.x users connect fine, only W2K (and XP)
users have the problem.
Any feedback would be appriciated.

Thanks,
Bill