You could try running Memtest86+ for a few passes to see if your RAM is bad. Any error indicates bad RAM. If you're running Win9x-era hardware, with 256MB of RAM, replacement memory (probably PC100/PC133) will not cost you much, AFAIK. You can get it from a dumpster PC to be honest, I have like a drawer of PC66/100/133 mostly.
You can write mt86+ to a floppy and boot to it: http://www.memtest.org/