I have a similar problem and may just have found the answer. I have 4Gb of Geil DDR2 6400 installed (The cheapest I could afford after a complete upgrade). It works very well withXP and Vista 32 but gives the random lock up problem we all know and love.

I went to the Crucial site and downloaded the Vista check tool and ran it. I immediately got a BSOS, tried again and got the same. Could be my attempt at saving a few quid is going to cost me more than I planned.

M/b EVGA 680i SLI
Intel Core 2 Duo E6850 3Ghz
Graphics EVGA 8600 GT
4 Gb Geill DDR2 6400 Ram
Vista Ultimate x 64

Your comments would be welcome

Looks like I will spending Xmas on the laptop (Vista x 64 NO PROBLEMS)