...and I have 376 mb of DDR2100 or 2700 ram.
Since you added this part after the initial post I'll respond to it now. Actually you have 384MB of Ram, your on-board video card is taking 8MB for itself. Look and see what the maximum amount of Ram your motherboard can handle before you look into buying more Ram for your system. Since you are running WinXP you going to want at least 512MB of Ram or more if you can. I wouldn't go more than 1024MB if your machine can even handle that much. Also look and see what type of Ram is in your machine now (2100 or 2700), you don't want to mix those two types of DDR Ram in your system.
BTW since you?re on-board video is only using 8MB of Ram. Any video card you stick into that system is going to make a huge performance difference. That on-board video is a serious bottleneck on your system. I'm surprised some of your games are even running with that. If you want to upgrade your system and not buy another one, I would suggest both a Ram and video card for your system. If you can only afford one upgrade at a time than I would go for the video card first. Hope this helps.