At this point you've installed XP and applied Microsoft updates. You've got your virus scanner installed and working. You have installed your applications and data and applied yet more updates from Microsoft for Office (if you have that). You're feeling pretty safe and secure.
Well, I've got one more tool for you to run. If everything was working well, you should be safe, but just in case, here's one last thing to know about.
The McAfee AVERT Stinger is a freely available program to scan your disk yet again to detect and remove specific viruses. If somehow something got through, this is your last chance to find it. Visit http://vil.nai.com/vil/stinger/ and download the binary. There's no fancy install, it's just one program so you should save it someplace where you'll find it. I always put it at C:\ so I don't have to rummage all over the place looking for it.
Find and double click on Stinger and click on 'Scan Now'. It's time for yet another scan of all your files. This'll take a while (5-30 minutes) so it's a good time for another break. If Stinger finds anything, it'll tell you about it and remove the file.
Once in a while (perhaps monthly), you should rerun Stinger and re-scan your entire machine again. Just in case - you can never be too safe, right?