What I recommend to you, and anybody else on TUG who cares about their data, is to buy an external hard disk
and some disk imaging software, such as Norton Ghost or Acronis TrueImage. I use something called EZ Gig II by Apricorn, because it was supplied free when I bought a drive from them. It looks and acts like Acronis.
Then, periodically create a full disk image of every hard drive on every computer in your home. I should do this weekly, try to get to it monthly, and in fact frequently go 3 months or longer between backups. My bad. Hopefully you can do better.
When you get it, do a full disk image backup just before installing SP3. If you have problems, you can use the backup software to go back to exactly what you had before. I've actually had to do this a couple of times when I've installed bad software, and had no problems in doing so.
It's also a nearly foolproof way to get rid of a virus. Just wipe the disk clean and go back to an image from before the virus. Of course, you lose everything else you've done in the mean time; but that may be an acceptable price.
I've been using this technique for years now. I only have a 300 GB external drive. But since the images are compressed, I can easily keep a half dozen or more images from each of our 3 computers (mine, hers, laptop), with space left over. 500GB and 1TB are available now at a reasonable cost, giving you even more room for multiple backups.