I work on thousands of computers.. (no joke, see me on TV <snip>I do computer repair for a living and have worked on over 6000 computers)
SP2 with XP is great. No problems, my old beat up laptop still boots in under 13 seconds and all my programs work just fine.
With SP3, about 5 out of 10 times it will not even install on XP.
Out of the 5 that did install, 100% of them are slower, 90% need more ram, 100% experiance weird problems and lock ups.
It's MS's way of getting you to "upgrade" to Vista.
Anyways, please let Paint.net work with SP2. :-)