Check out all these links before jumping in.
I have upgraded one of my AMD PC’s with little problem, except some intermitent problems with IE6. Pre install, I removed IE7 as suggested in the IE Blog (see below). This machine doesn’t have Norton Antivirus, and uses Trend IS 2008 without problems.
IE and Windows XP Service Pack 3
Norton software conflicts with Windows XP SP3
XP SP3 triggers false positives in security apps
HP recommends against installing Windows XP SP3
Don’t be in a hurry to install XP SP3
What you need to know before you install XP SP3
Does your AMD-based computer boot after installing XP SP3?