I'm afraid Norton 2001 is NOT compatible with XP, Dominic. I know, because I've tried it.
I've got a ghost image of XP/Sp1 which i created for easy formatting, but as soon as i load it, set net up i was getting that prob, i thought it was blast, but its W32.Welchia.Worm.
Now, this might sound stupid, but sometimes the obvious things are overlooked - are you certain you haven't got the Welchia worm in your ghost image?