To answer the original question, I have modern warfare 2 installed on my x64 windows computer and it works without flaw. Rest assured that you won't have any compatibility problems with the OS and game.
Another thing, where did you get the intel that mw1 doesn't work on win7? I also have CoD4 installed on my computer and it also works flawlessly. Also rest assured that you won't have any OS related problems.
And finally on a completely unrelated note, to address all of the mw2 haters and flamers:
DarkXeno said: "Why buy a PC game for online play if you cant host your own settings when you want to."
Incorrect. You can make a game with your own rules, allowing you to all of the options that was available for mw1.
Regarding scubasteve's essay on how crappy mw2 is:
1) no more community- well that's true, i'm not going to deny that. But only to a certain extent- there's the integration with steam that allows you to join groups and see who in that group is playing what. You still can have friends on modern warfare 2.
2) control over cheaters- again, there is truth in that statement but at least steam VAC at least has a chance over punkbuster which is virtually uselesss today. I've seen cheaters in both games- when there were cheaters in CoD4 (and there are a lot of them) they would usually be kicked pretty quickly. In mw2, i've only seen a couple of cheaters to be honest and it sucks when that happens. But I just leave that particular lobby I was joined in and start another match to get hooked up with other people. It really helps that cheating gets your steam account that you paid 60 dollars for permanantly banned. That's why there are so few cheaters in mw2.
3) Idiot control- again, this is true too. But again, it's not a big deal like what the essay is making it look. If there's annoying people on voice chat I simply mute them. People typing absurd things usually don't bother me, and anyways, I walk up to them and knife them in the balls while they type their long-winded insults.
4) Mods and custom maps- this is the one feature I do kinda miss. I don't have any counter-arguments for this, except for the fact that I never played mods on mw1 because they, for the most part, sucked pretty bad.
5) console- this too is a feature that I miss, but it's definietly not a dealbreaker.
6) leaning- big deal, suck it up big boy. Adapt to the new gameplay and move on for crying out loud!
7) Fluid gameplay- yes again there is definitely truth in this. Sometimes, when a peer with a bad internet connection hosts the game, the game gets all crappy. The game has a host migration feature that will automatically detect laggy gameplay and choose a new peer with the best latency and resume the game. It definitely sucks that the game gets suddenly paused and you have to wait that 10 seconds, but again this doesn't happen often (in my experience, once every 20 games or even less) Definitely not as bad as the little essay said it was.
I'm not saying that these problems don't exist. I'm just saying that it's not that bad as people are stating and you will definitely enjoy the game if you buy it.\
cheers....