Search the forums, this has been discussed.
Basically, be sure you're running the latest Parallels build (5608) and that Parallels Tools in XP have been upgraded to 5608 also, you have upgraded Boot Camp (if that's the case) to 2.1 (via Apple Software Update). If all the previous is true then you are prepared to upgrade to SP3.
For better clarification on this please use the search function on these forums to search for the relevant topics, as this has been widely discussed before.