I have an AMD 64 3000 (not sure about the +).
It's pretty nice, but I haven't switched the the 64-bit version of windows, since you can't run all the programs (mainly games) as with the 32-bit version.
My current CPU fan is an older version of
this.
Mine is all copper and, though big, it works great and looks awesome.
It's kindof big, but there's still room for everything else.
How much RAM do you have now?
RAM is a great way to speed up your computer for fairly cheap.
You can get some good deals on it online, if you know what kind to get.
I like to keep an eye on
www.edealsinfo.com, every once and awhile they'll have RAM for really cheap (like 512 DDR PC2700 for 30 bucks).
If you have the money, I suggest buying the best parts you can now and then you won't need to upgrade for awhle (2 - 3 years, is awhile for me when it comes to components).