Over at the Viperlair they have a guide up on how to make an Office XP CD with Integrated Service Pack 1.

The whole point of this exercise was to create a CD with Office XP with Service Pack 1. Should there be a Service Pack 2 (likely), this guide should apply to it as well, though I'll be sure to double check. I know some may be thinking that this is a lot of work, but think of it in the long run. You'll now have a backup of your original CD, since I hear a lot of dubious stories like "I lost my originals!!", as well as a backup of your CD key.