Thanks Saint. The first time I added the two 1GB sticks of 400 to my two 433's, the screen was flickering and the computer was acting weird. I had just reformatted and reinstalled XP onto a second HD. The flickering problem was actually due to a slightly dirty XP installation disc. I think some of the installation files were not quite right. I cleaned it with distilled water and wiped it out from the center with microfibre. Now it's running great.