you will be able to see icq and stuff on the second monitor while you play on your main.
however, you will need to taskswitch out of most games so you can access the other applications.
most games will minimize, and some can take a while to perform the taskswitch.
games that allow borderless window-mode are awesome for this, taskswitches take milliseconds and the game doesn't minimize.
some games also have crappy mouse capturing inside one monitor, so if you manage to click on the second monitor by accident, your game will minimize, which is pretty annoying.
like the previous poster said, you dont need eyefinity for this, just extended desktop.
but if you wish to do full-screen gaming on one monitor and want to keep the other display active - say, to eyeball some sort of status or watch videos - your displays have to be running the same resolution.
is this a newly introduced limitation of the new ati cards?
I was playing WoW in 1440*900 and had an extended desktop in 1024*768 since radeon 9700 times.
and also have no problems running a 1920*1080 HDTV in extended desktop additionaly to my triple setup 4320*900 on a 4850.