but you wont get any more updates for security till you do.
SP 2 not optional anymore
Microsoft to turn off SP2 download block feature
Microsoft will turn off a feature that allows some enterprises to block the downloading of its Service Pack 2 (SP2) security update for Windows XP.
This move will start from Tuesday, April 12, which means SP2 will be downloaded automatically to desktop computers that use Windows' Automatic Update feature.