share internet connection

I wanted to share my internet connection to 2 other pc's, one connected by ethernet and other by firewire (so just windows isn't enough for this). It must be a software solution, I don't want to buy a router, it must work like a nat server, no proxies, have a dhcp server and (the worst part) must work well with my firewall, sygate personal firewall pro. I've tried wingate, but it seems to have some problem with firewire. also tried kerio, but it has its own firewall and I saw no option to disable it (so I didn't even try to connect). any other ideas?