While there were a few who had problems with the WinXP service packs when they first were released, most of those problems have been worked through, and you should NOT have a problem with installing the SPs unless you have some SPECIFIC hardware or software that you must use and that is known to conflict. In most cases you'll be better off getting rid of the conflicting (usually obsolete) item and getting the SPs.

Microsoft currently downloads automatic update to MORE THAN 200,000,000 users EVERY MONTH, and you MUST have the service packs installed in order to receive automatic updates for WinXP. That's a pretty strong vote of confidence from the users.

Norton did have a problem when the first big SP was released. It could look pretty big if you weren't expecting it, but actually was not difficult to accomodate. If you had Norton Updates, it was corrected within a week or two of the first distribution of the SP for all Norton AV versions eligible for updating.

John