Im running 3 monitors using hybrid crossfire (on board + 4850) and whenever I launch any 3d app/game my other two monitors don't blackout I can still see the desktop on the other monitors. I'm using the default catalyst settings
Ive installed windows 7 using retail disk but with an oem key it worked fine you can always change the key from right clicking my computer-properties then selecting change product key
I found it to be really good you can kill enemies with head shots instantly and once you complete the main story you can carry on doing side quests that you didn't get complete or find. some mutants take a million shots to kill tho haha
I read somewhere a while back that the resolution should be the same on all 3 screens so it would probably work if you lowered the 1440x900 res monitor to 1360x768 but it may look a little odd.