Quad monitor, dual computer issue

I've got a little issue driving me slightly up the wall, linked is the monitor setup I'm using. I can go from computer 1 to computer 2 and back no problem, as long as it's on the #1 (as labeled by windows) monitor. I can go from the Primary (#1) computer to the secondary with no issue on the primary monitor, but I can't drop back down until I go over to the #1 monitor side.

Both systems running Windows XP and the free version of Multiplicity