Thanks for the replies, all.
Yes, I do have Spyware S&D as well as Ad-Aware. Been too long since I ran them, however, as I had quite a few cases it turns out.
However, after running memtest for 3 days in a row, 8 hours a day, I finally found an error. I guess I'm going to have to have to pull one stick out at a time to see if I can find which stick is having the problem, now. This isn't going to be fun.