Invalid page faults, stack errors, memory issues

I have been getting invalid page faults in both Excel and AOL - I have refurbished Dimension L400 - i have 128 meg ram. I have already gone into msconfig and gotten rid of unnecessary items in selective startup, I was told by an @home technician that I probably have a bad memory chip or bios problem because he kept getting different readings on the amount of memory. Any new ideas?