West2009,
Thank you for contacting the Live OneCare program forum. On your XP operating system, run this tool to uninstall OneCare.
Uninstall running this clean-up tool:
http://download.microsoft.com/download/4/c/b/4cb845e7-1076-437b-852a-7842a8ab13c8/OneCareCleanUp.exe
Then load Vista and reinstalling OneCare directly from the OneCare website. First install the trial, then click Activate. Then enter Live ID.
I hope this information helps. Thank you for contacting the Live OneCare program forum.
Rick, MS