I had something slightly similar with the win7 RC before I had to shell out for a retail version of home premium. Maybe problem was I had not paired the RAMs (2 x 1gb, 2 x 2gb) together properly as the motherboard colour-coding was REALLY misleading/rubbish. In the end I replaced the 2 x 1gb with 2x2 giving me 8 and paired them properly. No crashes in 3 months.