DISCLAIMER: The process described in the second paragraph is not a panacea!!!
Following the some of the other suggestions here, clean out your system of unwanted/unneeded software. Find yourself a good registry cleaner and scrub your registry well. You can oogle one. For the most part any one is as good as another... So long as it isn't laden with malware. Anyway, the page defrag tool from Sysinternals is a good idea, just make sure your swap file isn't variable in size (i.e. managed by windows). Setting a fixed size insures you swap file won't (well, shouldn't) fragment.
After that's done, if you're still not satisfied with your system's performance, you can try a repair install. It blows out (for the most part) the System hive of the registry while retaining the user hive(s), while retaining the registry info for your installed apps. However, you'll have to apply all the service packs/hotfixes not included on your Windows CD... That is unless you slipstream them ,
nLite will help with that (also make sure you do
this).
Please keep in mind that this process can also introduce a few idiosyncrasies and may require some tweaking afterward. I've done this a couple times with both 2k and XP and it has improved performance somewhat. But as I said in the disclaimer, it's not a panacea. If your performance problems stem from 'third party' software (i.e. not Microsoft's core OS files), this process will probably not improve things much.
