I have run memtest86, I said that in my initial post, for an extensive period and no errors were found.
But I will still try and put the old mems back and see if the problem goes away. Might just be a bad combination with 1066MHz mems for an 800MHz CPU even the memory is clocked at 800.
Stranger things have happened with computers so..
It might just be the newest ATI drivers as well.. when thinking about it I can't recall having this BSOD before I installed 8.4. I'll continue to try and find the reason. Might have to do a complete re-install as well.
However, I suspect myself that it's the Creative X-Fi Music that's the real cause... nothing has ever worked well with it since I got it, not in this or the old computer.. and the drivers are, if I put it kindly, pure crap.