Redhat 9 and Winxp. Although now with redhat getting out of the consumer market and leaving only the Fedora project, which I heard some pretty bad reviews, i'm seriously considering debian.
Debian, specifically Sarge (testing) on a an old 333MHz box, dual-homed, with an rfc 1918 network behind it (where the rest of my machines are located) and running iptables. In front is Comcast's cable modem drop.