Well tried a few more things and still can't get to the bottome of it.
Task manager shows pretty much the same stated figures as above all but 10 or 20 meg in the text prtion on the right but at the bottom and in the graph it now shows 32% usage.
Perfmon and nvidia both state the same figures.
tried booting to safe mode with networking and had a freeze there too
Tried safe mode without networking and was stable for around 2-3 hours with no crash.
Re ran vista's mem test with a higher number of passes which did not flag anything.
Ran scandisc and again found nothing
Also tried a sfc /scannow form the command line to again check for corrupted files and found nothing.
Seems so intermittent i can't put my finger on it
Sometimes am ok for 2-3 hours and at others 2-3 mins.
Starting to wonder if another reinstall is gonna be the way to go to try and rule out any possible updates as the cause.
Hard drive activity seems to be less though but think i may be clutching at straws here.
Can't really see it as a hardware issue as if it was surely i would see it crash at around the same time each boot.
Don't suppose it would indicate my power supply is on the way out
Other than that the only things i have left to try is a different keyboard,monitor or unplugging the router supplied by sky but again can't see that they are the cause as they work after a reboot.
Don't see any hardware failures in the reliability monitor.
Other than that am at a loss as to what could be causing the issue.