I also ran into a weird situation on my machine. It was under Windows 7 but that probably didn't make any difference.
I have 4 sticks in two banks, all exactly the same modules. During testing (was having the HD light freeze problem) I took two sticks out. No change. Swapped sticks. No change, then put the other two sticks back in and the machine would randomly crash hard and often. The sticks were in reversed banks to the way they had been but properly installed. I took the sticks out and swappend the pairs back into their original banks and had no more crashing problems... (Still had the HD freeze but figured thatout later).
As google recently reported, flakey ram behavior is far FAR more common than anyone previously thought. Like at least an order of magnitude worse (10 times as many problems caused by intermittant or bad ram than anyone thought).