As Mike mentioned above, first check for any upgraded drivers for your mouse & also check for updates to your game, in fact every application you're running. Zip over to the Microsoft Update website & check for updates & patches (in fact, do this at least once a month since Microsoft issues new updates every month, second Tuesday.). Once you're done updating EVERYTHING then check with your applications tech. support if you're still having problems.
Your system hardward is sufficient to be running Vista so you shouldn't have to worry about that being an issue (though I get a kick out of all these ads from Intel & AMD about dual+ processors. In home PC's they are mostly useless simply because there are so few applications that utilize dual or above cores. That is changing, of course, mostly in the gaming world.).
I'm not going to get involved in any Windows/Apple/Linux discussion because all 3 have their good points & bad. Do you want to run everything (meaning applications) with no problems (meaning compatibility), then Windows is the answer. Graphics are your thing, go with Apple. Don't like mega-corps. & want to try something different, Linux in all of its flavors may be for you.
Oops, my take on Vista: don't bother unless you're forced to. There truly is no compelling reason to do so. I'm not saying Vista sucks (please remember the hue & cry when XP first came out) there just isn't any reason to spend all that money on an op. system that isn't dazzling. In order for me to do my job from home I'd require Vista Ultimate; ain't gonna happen as long as my XP is stable & happily chugging along.