If only I'd checked in here and read these recommendations before I encountered more memory problems. Unfortunately the system crashed today and in the process of sorting it out I cleverly manged to wipe the parallels partition. So I've now lost my only copy of XP and all the other car pc stuff that was on there.
Still on the bright side, I've decided to upgrade to Leopard and use bootcamp instead of parallels so hopefully won't encounter quite so many memory problems as I did with parallels.
Any hot recommends for running XP on bootcamp, particularly in reducing boot times and optimising the speed?