Just to update you all - the blue screen of death was down to nvidia drivers nvlmm*.sys.

A common problem it seems. I tried loads of things, including getting various different drivers (even going to beta).

I turned off vista 64's insistence on properly signed drivers, and that didn't help.

I was checking in the bios when I noticed that cpu overclocking was set to auto, I took it off of auto and set it to the next option (would have gone on to the 2nd option if that failed) but all of a sudden the system booted up.

So I presume that the autoclocking mode was stressing out the graphics card so all was working well. I managed to install a set of usb dongle drivers that someone had modified (not an official release) and got the pc running.

Thanks for the suggestions. I will look in to upgrading the motherboard drivers.