Actually, Microsoft's defrag is a lite version of Diskeeper these days. A good one I use is VoptXP from
www.goldenbow.com . As for why your computer keeps telling you the HD needs to be defragged, could it be that it's nearly full? In that case it's near impossible to really rearrange files, especially large ones like, say, DivX movies.
Likely reasons for general slowdowns in XP (as observed by me personally) - cannot speak for 2K here:
* not enough RAM. Even 256MB is rather on the low end, so I quickly upped mine to 512MB.
* Indexing service is enabled. Stop and disable it through Services Manager. Then rightclick each HD partition in Explorer and uncheck "Allow file indexing", apply to all files and folders when asked.
* Service Pack 1 introduces a bug that would slow WinXP down. There is a post-SP1 hotfix for this.
* System Restore can cause the HD to fill up rapidly. Delete all but the most recent restore points. Often, restore points will be set automatically by at least Windows Update and by setups using Windows Installer (.msi packages), possibly other apps as well.
On a side note, it might be a good idea to turn System Restore OFF on all partitions except the system partition, since there really is no point in maintaining restore points on storage, backup or pagefile partitions.
I have an SBLive! 5.1 by the way. Its drivers have never given me any trouble. I avoid downloading them from Creative, though, instead I use the ones provided with Windows. Since I bought my new PC this summer, there's actually been one driver update for SBLive cards on Windows Update which I installed. Not a single problem with sound here.