Like screwtech02 said above - widescreenfixer is always an option.  I use it nightly when playing MW3 online and have for a year now without issue.

Its free as well, though donating to the dev is always appreciated I am sure.  I have sent some $$ to him out of appreciation, simply because what he does is what the developers of the game should have, and that is allow it to work on widescreen resolutions above 2560x1200 or whatever.

When you are working at 5760x1080 and larger, most games out there were not coded to handle that wide of resolution, most PC's could not render that in a playable way either, so us triple monitor gamers are in a corner by ourselves.  This is why widescreenfixer has helped out a lot and I suspect it will again for Black Ops II.