Hmm, sorry to hear this. Don't see how its hardware though if you can install Vista. And U have used 7 RC as well. Have u tried to re-install the RC just because you can ?? And you are certain the HASHES for the 7 iso's you have are correct. Maybe try downloading Ultimate form the 1st page of Opa's guide, and give that a go. I KNOW those binaries/hashes are 100% good. You said a memory check was all good. Maybe want to rerun that too? Sorry I cant help further, but I'm stuffed.
Try wiping the partition you are installing it on first... leftover files although not visable are still there and will often screw a new install if the partition isn't wiped first. Technically it shouldn't matter, but it has caused me trouble on numerous occasions.