How did you install SP2 over itself?
I don't think Windows Updates will allow you to do that.
It is possible that SP2 never installed the first time.
First of all, you said that you are relatively new to computers. If that is the case I highly suggest that you do not use any third party programs that alter the registry or delete anything from it. Even CCleaner, which is considered to be one of the "safer" registry cleaners depends on your knowledge of what actually belongs or doesn't belong in the registry and use of these kinds of aps will eventually hose your op system because of a mistake you make.
Instead of any of the third party registry altering applications, I suggest you use only the following on-line scan from Microsoft:
Windows One Care Free Scan
Go to Windows Live Onecare Free Scan
It will say "Get a free PC safety scan"http://safety.live.com/site/en-us/default.htm
Make sure you click "Full Service Scan"
in the middle of the page and not the "Try It Now Free" on the right side.
Allow it to download the Active X components.
Choose "Complete Scan" in the window that opens
Do not click on anything else that offers you a free trial or to sign up if you live in the US.
Allow it to scan - it may take quite, maybe two hours or so depending on how big your hard drive is and how fragmented your registry and hard drive are.
If you buy a major brand retail hard drive it will most likely come with software that will allow you to transfer everything from your present hard drive to the new one thereby eliminating your need to reinstall Windows XP and redo all the updates since your Windows XP Installation cd (if you have one) or your manufacturer's restore cd was issued.
If you do not have one or the other, either the Windows XP Installation cd or the Manufacturer's Restore cd, I suggest you start trying to find or replace it now, before a problem may occur when you need it.
If you decide to get a viable hard drive I suggest a hard drive made by Seagate because it is the only one that comes with a five year warranty.
If for any reason the software cd does not come with your new hard drive, the tools to enable you to format the drive and transfer everything from one drive to the other are downloadable from most major hard drive manufacturers.