VPN user auditing

Our company has a remote office that connects to our domain via VOIP and VPN connection. We want to audit any logon/logoff events for 2 users. We are using Windows 2000 SBS Server as our DC. Builtin auditing does not pick up the VPN logon’s, and we have also tried Dameware software, but that does not work either. So the question is: how do you audit VPN users?