I have memtest86, and I run that every single time I get new RAM. I just installed new Corsair Dominators 2x2GB PC2-8500 Ram last night and did 3 hours of Memtest.. thats your first thing you should do with new RAM.
second. just like smarteye said. you should enter the BIOS and see if the RAM is being overvolted. you said that Crucial sent you new ram that takes lower voltage. but it doesn't just "take" it. lower means it can run with less.. you still need to enter the BIOS, and change the voltage to the Specified voltage amount. if the package says 2.1v then put it to 2.1 and if it says 2.0v then change it to that.. Overvolting the ram to 2.2 or more over time will always kill the RAM. also if it is the motherboard thats killing the RAM.. and it's not the voltage problem. then the only fix would be to get a new Motherboard. if the Mobo is killing ram, then it's NO good.. sorry to tell ya.
Heat is the number #1 threat to PC components.. so get a better cooler, more fans and the entire system will be happy. Ram can go faster when it's cooler, and same can the CPU. lol.
Download memtest to a disk, and boot the PC into the disk right after you get new ram. let it run over 2 hours. some say overnight.. and if there's any errors. return for a refund and get more.
good luck. let us know how this goes.