well I can see that 360-PC gameing may be possible, as with Tunneling the Computer seems to be capable of "tricking" the XBOX/XBOX360 into Thinking that there is another system on the Lan.
Now I'm not sure about this but do these tunneling services have all the data that go's in/out of the consoles travel through the PC? or does the software kinda like just devert any data in the network from the console to think that it's using Lan instand of Wan?
but I'm thinking that some kinda app for the PC will have to be thought up, 1 that can convert the signals from each machine and connect the 2, would be neat if they could input some mic support into it, like have the app be capable of picking up and sending the mic signals seperate from other gamecode, and on the PC have the user be able to use say a USB headset or somthin, best bet would be to go to a big quake community and talk about this such thing, and heck since we have quake2 on the XBOX(ported versions) maybe even ask about the possibility to interconnect all 3 machines, kinda like how the guy porting Quake3 has support between the XBOX and PC in mind for online play