Memory upgrade. I was given a computer. When I got the computer it only had one sdramm memory

Question

I was given a computer. When I got the computer it only had one sdramm memory chip. It was 128kb. I have no Idea of the manufacture of the motherboard. The only information i can find on the board is a number. M266. I am presently running two 128kb 133mhz sdr ships. So I only have 256k of memory. I would like to upgrade to at least 512k ddr. I am not sure though of how much memory the board will take. It was suggested to me to get a 512kb ddr chip, speed 166mhz. What do you suggest I do. I am running windows xp.

When I got the computer. It had windows 2000 onit. I formated the hard drive and put windowsxp on it. It runs okay. However it is running slow, and windows has to keep warning me that Iam running low on memory.