You mentioned that you had a server you could use for hosting the VPN... I'm not sure if it's already running applications/services, or if you're able to assign only the VPN functions to it.
If the machine is able to be re-used, I very much recommend a small firewall distro, such as IPCop, which is linux-based (
http://ipcop.sourceforge.net) or pfSense, which is FreeBSD-based (
http://www.pfsense.org). Both have rather easy-to-configure graphical interfaces to configure a VPN endpoint (standalone) or site-to-site tunnel.
The OpenVPN GUI (client) is much easier to use in Windoze than the command-line-only one. It's available at
http://www.openvpn.se . I've been using it for years along with a pfSense box and it's been rock solid--even with novice computer users.
There are active community-supported forums for both IPCop and pfSense, along with lots of documentation for each. I imagine it would be much easier to set up a VPN tunnel using one of these firewall distro's rather than attempting to configure it by hand on an existing linux server.
If you're needing something that installs on a currently-running box I'm not sure what to recommend on that... but it might be worth digging up an old P2/P3 box to dedicate to one of these firewall distro's, to make life a little easier...
Hope this helps.