Okay, I've given up setting up a VPN using this guy's equipment. You can't enable the VPN snap-in if you have ICS enabled on the server, which he does. I made an executive decision, and decided that I'd have to completely rework his network (which has other people who sublease office space from him), and the downtime needed to do that was not going to be satisfactory to this guy.

So I downloaded and set up LogMeIn's Hamachi service, which had me set up with a VPN in a matter of minutes. It's free for non-commercial use, so it's up to him if he wants to pay the $200 a year to keep it up.

Just thought I'd update with the situation.

*edit*
By the way, I don't suppose there's any way at all to share files in Windows across workgroups, is there?