Alrighty...here's the update.

After much cussing and swearing, i finally got ATI Control Center to recognize both monitors.

Selecting horizontal stretch across both monitors, however, does not seem to be the solution.

A) Two different size monitors (coupled with one widescreen and one regular) make for very odd stretching.

B) In game, FPS still sat around 12-15 while running two players around IF.

I'm going to continue fiddling with it, see if I can't make it at least more tolerable.