Wondering how to do this?

Here's the home office setup.

Two PC's each with a dual DVI out nVidia card. One primary SW/cad PC, one secondary browser/email PC

Two monitors.

Primary CAD PC running dual screens

Secondary PC running one screen.

The primary CAD PC runs the dual screens with one as a home screen and the other as the 2nd screen.

Want to be able to switch the 2nd screen monitor between the CAD PC and the browser PC.

Tried an IOGEAR DVI switch but it can't deal with a dual screen PC, it tries to switch the home screen monitor, and it doesn't work unless the mice and keyboards are connected and I don't want to switch those.

What I need is a simple switch that only switches the monitor.