WIN2K SVR RRAS VPN behind a firewall.

Gentlemen;
If I want to set up a VPN using WIN2K RRAS in a single server environment behind a firewall is it wise to use PPTP to keep it simple and how do I get around routing traffic with only 1 NIC in the server (RRAS seems to want 2 NICS)? I can’t have 2 NIC’s in the server on the same subnet can I? All of the documentation I have found talks about having 2 NIC’s (1 private side, 1 public side), but my server does not have direct access to the internet since it is behind the firewall. Couldone of you guru’s offer some help to a newbie, please?