Computer Restarting using DSl and streaming video

Hi I Have Windows 2000 On an Athlon XP 1900 with an Nforce 6373 motherboard. I have had problems using two 512mb of 2.5 cas latecy ram that runs at 266mhz. I boot up with 256mb of cas 2.0 latency ram and than in the bios I change the cas latency form autodetect to 2.5 and the cas 2.5 ram works. I have tried the computer and it works good with my cablemodem and stuff. Heres the problem I set up this computer at a friends house who has DSl. It works fine but after 1 to 2 hours the computer restarts when he is streaming video and he said it does a timed system memory check. What is causing this I have never seen this message before. Will a bios update help or using sandrsoft to stress the memory. Should I change the swap file

thanks guys

maybe its not the dsl that's causng it.

bad memory stick?