Throwing out possibilities to consider:
Bad DVDRW or scratches on Vista Installation DVD.
Diagnose Hardware problems, HDD, Memory, and eliminate them as being the problem.
You list 2G of ram but no brand, and sometimes the timings and voltage setings are off especially with OCZ modules, requiring you to set them manually, is that a black edition CPU?
Just trying to get a feel for what you've already done and checked?