Well the problem is that the netcode is often changed to be compatible with XBOX live, etc. Otherwise there *are* bridging programs that allow you to connect several XBOXs together over the Internet (using a computer to sniff the packets). There are probably a few games that have close enough netcode that the PC would recognize it, in which case it probably wouldn't be that difficult to make minor modifications to these bridging software to allow PC support, but one would need access to the source code
-DSR