SORTED SORTED SORTED (well for me)
Deciding this was not going to beat me, I set about a like for like (except the vidoe card) component replacement until the problem was solved. The video card was changed from a Nvidia to an ATi to no avail so i I bought a new motherboard, then a PSU .....
and finally the RAM ....BINGO. The previous RAM was 4gb Corsair and never once failed a memtest however replacing both sticks like for like & problem has totally gone.
So having all the new bits, I bought another CPU, hard disk & cooler and built a second system identical to the first one (except for the video card) I used the old RAM but instead of windows 7 I installed XP and low and behold........no errors.
Conclusion ........ windows 7 (64 bit) is very sensitive to the RAM. At some point in accessing the memory it triggers the TDR which we all see. Although this thread is now 20 odd pages long if you go back and read it again there are a lot of individual
solutions but "replacement Ram" crops up repeatedly. RAM is cheap at the moment (£25 for 4GB) so it's got to be worth a try for everyone else out there with this problem.
Hope this helps someone
JR - happy puppy, smaller wallet but 2 working PC's :)