tftv256's suggestion (mirroring input devices to each console via TCP/IP) would not work well except over a tiny LAN, where it would be pretty much superfluous. Console games depend on input device latency of less than 10 ms. Good luck getting that kind of ping time over any nontrivial connection (DSL, cable, dial-up modem). The games will fall out of sync even before the game starts. Besides, the random number generators on both consoles will not be seeded the same, resulting in random events (item respawn, player respawn locations, hits and misses) falling way out of sync. You really need a game designed for client/server. These have appeared on at least the Dreamcast, the PlayStation 2, and the Xbox.