In the Seattle P-I, Dan Richman has written a well-balanced piece on SP2, “Microsoft’s SP2: A fix that derails some computers.” I’d say the single most important sentence in the story is this piece of advice:
Don’t give up. The protection it offers is worth the pain it may cause.
On a healthy PC, SP2 should install quickly and without incident. In unbiased surveys, I’ve seen indications that more than 90% of the people who install SP2 have no issues at all, and my personal experience matches that figure. If you’re experiencing problems with SP2, those are warning signs that something is wrong with your computer. If you ignore those signs and just decide to deal with them by uninstalling SP2, your PC is a ticking time bomb. A far better strategy is to find out what the problem is and fix it.
If you’ve successfully installed SP2 and you want more information about how to work with it, consider picking up a copy of Windows XP Inside Out, Second Edition. If you’re an IT professional or you work with corporate networks, pick up the Deluxe Edition. Carl Siechert, Craig Stinson, and I worked with SP2 throughout the best testing cycle and have lots of good information on how it works and how to work with it.
Ed Bott 
Ed, I’m writing for some advice for my Dad who has had trouble installing SP2. He claims an article in the Seattle Times led him to a support number based in Nova Scotia (?). If this sounds familiar, can you give me more contact info, as I’d like to see if we can save his data before reformatting… his computer is a doorstop at the moment. Thank you!
Based on an email exchange, it sounds like the issue Elizabeth’s dad is dealing with is the BIOS problem with certain variants of the Pentium 4. The support folks should be able to work this one out very quickly for him.