Is it possible to connect one PC to another PC and have the first PC emulate a USB device for the second PC? Does this cause terrible explosions having two USB buses plugged into eachother? The situation here is that I want the PC to pretend to be an XBox controller so that I can write fancier automated test cases.

To connect two computers together you will need a USB bridge. A USB Peer to Peer cable for file and hardware sharing or a USB Data Transfer Cable for file sharing. CAUTION: Using A to A USB cables, will short the two PCs' power supplies together, possibly destroying one or both machines or causing a fire hazard.

Dunno if it supports ANY usb/usb connection, but it definitely DOES do pc networking.

If you want the target PC to be able to emulate an arbitrary USB gadget, you'll need extra USB target hardware for the PC. I don't know whether that even exists. You'd be much better off using a car-player, possibly with a newer kernel to take advantage of all the new USB gadget stuff that's gone in recently.

Peter