No real reason to get a new cpu cooler if you've got 2.9 anyway.. In the best cases, it won't go above 3.2 so unless you have really high temps right now... waste of money
I agree with Coffee that these games don't really need a good mouse. Oblivion doesn't need a good one at all while Halo is just... not really too important.
I would just save up a bit more and get a sound card. An audigy se isn't
that much of a difference so with an X-Fi or something. You can probably find an XtremeGamer for $60 or so from a good deal or an XtremeMusic used for like $50 if you look around. Although if your speakers/headphones are crap you can pretty much throw that out the window too
.