I assume that you reinstalled OneCare on the desktop at some point, hence the reason for the extra entry in the list of computers when you go to the Manage your OneCare Circle on a hub PC and you have apparently made both of your computers into hub PCs. Simply highlight the entry for the desktop PC that shows a last status date of some time in the past - this would be the ghost entry - and click remove this PC. You only need do this on one of the PCs and your Circle will update on both.
I'm moving your post to the Multi-PC Management folder.
-steve