Sorry for the delayed response but it resolved itself BIG time in the early hours of this morning.
After I had checked in the logs as you suggested Adept,I couldnt find anything that looked like the cause.Sometime later my adsl connection dropped me and wouldnt re synchronise for a few minutes.I reconnected only for it to drop it again 5 minutes later and it refused to re sync at all.
I rebooted to see if that would sort it out 8)
My PC didnt manage to start windows again
I got the dumping physical memory thing and after a couple of attempts tried to start it in safe mode.It wouldnt do that,wouldnt do the go back to last one that worked thing either.
I tried repairing XP with the installation cd but for some reason as it got to the point where it asks for regional settings (or about 30 seconds before) the screen just went blank and the installation/repair stopped.I repeated the process ( I am nothing if not stubborn
) and it stopped at the same point again >
At 4 am I decided it was too late to resolve it so I left it and went to bed :'(
As I was still having it wanting to dual boot,even though I now only had XP on,I decided to wipe all the drive and being a bit masochistic used the seagate wizard utility to do a zero fill on the full drive.
Everythings back on and working fine now but I guess the reasons for what and why it did it will always be a mystery