Put the PC and guts in 1 of the machines, and build a player1 CP on that cabinet
Build the player2 CO on the second cab, using longer wires to connect it to the Ipac in cabinet 1
Find a way to duplicate the video signal to go to both monitors(Im sure there are ATI cards that'll support 2 tv-out connections)
Now youve got connected cabinets, with a single cable between them(assuming you wrap the individual wires into one)
The Need for SPeed series on PC is pretty cool on lan. Me n a buddy play on 2 pcs, one is his HTPC going to tv. Looks fine in 800x600 and very playable in 640x480