Win2k VPN Server questions

[DentyCracker]

Trying to setup a VPN Server here at work. Hardware is a Dell Poweredge 1600SC Dual Xeon 1800 with 512 MB RAM. This machine is running as Domain Controller. This machine also has MSExchange 2000 installed. It is also the Internet server, setup to do NAT and DHCP for the LAN here at the head office. Connectivity is through an Alcatel SpeedTouch USB modem via PPPOA DSL that is set up as a demand-dial connection in RAS. Internet connectivity works well as it is a realtively small LAN (18 users). We don't have a fixed ip address (too expensive), but I have a dyndns.org address for the server that is updated regularly. I can't login from home, even after I have just updated the name, I get error 619. I also get error 619 if I try to login from some of the machines at work. I can login from some of the machines at work, notably those that were not recently added. I suspect that there may be some policy blocking access from certain machines. I have tried it with or without the firewall and no change in behaviour. Any ideas? Not running RADIUS authentication, only MSCHAP v2 on both client and server. Only one user has dialup access enabled and that is the user/pass I use on the client login. Is there extra hardware that I need to buy? Any help is appreciated.