If you're running Windows XP with Service Pack 2 or even Service Pack 3, what happens if you have to perform a system recovery using your original XP CD? Hassles, that's what.
Reader Ralph recently experienced that exact scenario, resulting in an awful lot of Windows Updating after the installation. That's because the old CD doesn't have all the patches and updates you've downloaded over the years. It could take hours or even days to re-download and reinstall all that extra stuff, during which time your PC is more vulnerable to viruses and outside attacks. (A lot of those patches tackle security issues.)
Consequently, Ralph wanted to know if there was some way to back up the Windows Service Packs so he wouldn't be in the same boat next time.
There is--you can download the Service Packs as standalone installers directly from Microsoft (here's SP3, for example)--but I propose a different solution: slipstreaming.
Slipstreaming is the process of combining your existing Windows XP CD and the latest Service Pack into a new CD. When you're done, you'll be able to install Windows XP with SP3 outright.
This is easier to accomplish than you might think, provided you've got your original CD and the aforementioned standalone Service Pack. However, I'm not going to repeat the details here; check out Lincoln Spector's Slipstreaming Service Pack 2 on an Old Windows XP CD. Just substitute SP3 for SP2 and you're golden.