You can get adapters that allow you to use a PC mouse/keyboard on consoles, though they can be pricey and Im not sure if there are some restrictions on which keys are supported in games.
Personally, I dont think consoles are suited to FPS games, lower graphic detail, larger hit boxes (to balance out controller response/accuracy issues), paid for DLC, auto-aim to hold your hand while you play...not as challenging/rewarding as playing on a PC.
Microsoft had a cross-platform beta FPS programme a while back that supported cross-platform multiplayer. The PC players laid waste to their console rivals, not necessarily because they where better players, but purely because the PC had better more responsive/accurate input devices....needless to say Microsoft put that project to bed.
The good news about COD: Black Ops is that they have confirmed dedicated servers on the PC, but only through a single game service provider (GSP) so far, so its not looking likely that there will be any community server-side-mods which would seem to suggest they are following the paid-for-DLC path to new content on the PC (console users wont be suprised by this as they bend over and take it without a whimper).
Someone earlier mention they'd prefer a more realistic FPS, if you want a realistic milsim, get a good PC and get Arma 2/Arma2 Operation Arrowhead, forget about Operation Flashpoint DragonFailing, it is utter crap and no closer to being a milsim than mario cart (also the latest patch on the PC can cause your graphic card to fail). If you want a realistic counter-terrorism game, go for Rainbow Six: Ravenshield (with the Iron Wrath expansion pack) - an old game, but a classic with no rival to date.