Memory Problem

Hello all you wonderful techies, I am having some problems with my computer freezing and I believe it is a ram issue. Recently my computer has been randomly freezing and I could not figure it out...But I just now did some "tests" and figured out that if I open 6 programs my comp freezes??? Before this started happening I was getting memory errors saying it couldn't access " *lots of numbers* " memory, or something similar. I am very tempted to reformat and just reinstall windows xp and start off with a clean slate. Most of the things on my computer can be easily saved and reinstalled. Plus I have not reformatted ever in about one and a half years (when I bought it) soooo it may be a good idea.....Or could this be that my memory is dieing and I need a new set?

I have one question that I was thinking of though that may cause a problem. I recently renewed my one-year subscription to Norton Antivirus, and if I reformatted and reinstalled Norton would it automatically pick up where it left off?

Gigabyte Ga-7n400L1 mobo
Amd Tbred 2700 cpu
512 mb 2100 cas 2 (mushkin I think) ram
400w Sparkle PSU
g4 4200 graphics card

If you need any more info please ask, this problem is really bugging me.

run memtest for about an hour that will tell u if its the ram could u also say what fsb u are running at

I am running at all stock right now to try to figure this out, so 13x166.

well u have pc2100 ram (133fsb) and thats only good for about 150fsb so it properly is the ram run memtest for about an hour tho to make sure