I'd go with one of the firewall/gateway/router/NAT/DHCP boxes out there from Linksys, D-Link, SMC, etc. Extremely simple to setup, little to no maintenance, and PPTP and L2TP VPNs seem to work just fine over them. Very reliable, and pretty cheap at $100ish.
They generally have a 4 port 100bT switch on them, too, so it's really a plug and play deal.
Plus you're not putting either machine directly on the 'net. :)