It seems that I finally found the problem in my pcs faulty behavior. After experiencing a lot of BSoDs with the id for critical hardware failure - it seems that the failing part was detected Look at the image... the capacitor blew up and just eroded. Guess that was the reason for an unstable powersupply and henceforth the reason for failing memory and the crash of the system all the time.
So what's the deal... I guess I will have to buy a new one as it is virtually impossible to get a new MB for Rimmbus Ram modules anymore. Thus meaning I also need to buy a new GPU ( as newer boards rarely have AGP slots ) and so on... oh well... guess this will be some expensive thing to do.