Sciencewiz -
I ran PC Doctor and all the memory test when I had the crucial 512K and it passed fine. yet,
I was just having problems mostly application crashes and sometimes complete windows crash
about once a week.
After taking out fine for 3 weeks and I did have 1 crash, but none since. So hard to be 100%
absolute on this, but the frequency of crashed is gone.
one thin crucial did pass on was to mak sure you increase(double) the amount of virtual ram
you allocate when you add memory and reboot.