I have experience with running Cubase on both of them, with or without my mate sitting in the right chair.
Now I plan to do all editing/sounds on one computer, and use the other one as sequencer. This would totally solve sync problems. But, my Rewire setup runs on the heaviest pc. This pc on a dual PIII 1GHz would also be my synth/sampler/fx/mixers pool. And the slower pc would sequence. It's too light for Rewire. I should abandon Rewire for these projects.
DeFex showed me much more convenient hardware solution to '2 computers on one screenset, keyb and mouse'. It's a switchbox, which has simple turn knobs and swithes video/keyb/mouse from one pc to another. This is a way more solid setup, and allows you to keep dual monitors
atomic.