Well, my VPN took a about an hour to sort out, here's what I have:
At home I use XP's built-in VPN client. At work I have an IPcop firewall (
www.ipcop.org) - this is a Linux firewall distro that I have serving 9 UK domains. I setup a Win2k server as a RRAS server, using domain authentication via a policy setup in AD. The firewall forwards GRE & tcp 1723 to the RRAS server (PPTP connection). That's it, job done. I'm working on using certificates to authenticate next, so I can use L2TP, just having probes getting XP to use them :-(
Oh, I only use one nic on the server cos otherwise I lose domain visibility, contrary to what MS says, this works fine. (I think u'd need the two nic scenario if the server was internet facing, and u would have to use the filters RRAS sets up for u). This setup has been working flawlessly (and securely) for the last 8 months.