are they both 21" ? I've got that going on right now and it's sweet…very much required if you're doing lots of OTL stuff > houdini in one monitor, all the otl windows (type prop. edit contents etc) in the other…
I have it working well in windows with my gforce fx 5900 when I am in “stretched desktop” (one desktop stretch across to monitors). I get GL glitches when I am in “dual monitors” mode. The only problem with stretched screen is things tend to pop up on the seam between the screens. But it is easy to switch between single dual and stretched.
At some stage I will try to get it working in Linux.