Success!
i tried swapping ram (memory chip) with one from another computer and that appears to have solved the problem,
computer boots up normally now.
So Memtest was a great idea
and
Knoppix proved very helpful in allowing this to run.

Thanks for the help guys.

Matt

re : "removing a bad strip" do you mean prying off one of those black rectangles (there are 8 on each side) of my 512 mb DDR 400Mhz CL3 RAM thing? I might look into that if i have time..