Sorry, didn't realise you were still having trouble with this.
If Vista installs ok , but 7 doesn't - even if you install it on it's own, then it is probably not a hardware problem.
Sounds like it is either the iso , the burn itself, or the dvd.
I would burn the iso again using a program that controls the buffer well. This is a good free one http://www.deepburner.com/download/DeepBurner1.exe
It's very simple click Create iso image in the Help file and follow that. Leave the default speed setting - it says Max, but controls the speed auto. so it "stays behind the buffer."
If you still have a problem , then you need to d/l another iso.
Hope it helps