You will need to know what type of ram you need for your computer. Hopefully there will be a sticker on the ram in your computer telling you what it is. It may say it is DDR266, DDR333, or DDR400. Or it may say it is PC2100, PC2700, or PC3200. These correspond to each other. DDR266 is the same as PC2100, etc. When you know what to buy get a stick of 256Mb and just install it in the computer. If you are carefull you will notice it can only go in one way. It is a very tight fit so make sure the side pins lock the memory in.Once you install the memory just boot up the computer and it should say there is 512Mb of memory if you go to the system window. By the way, 512 Mb is the sweet spot for memory in WinXP. This computer is using 226 MB of memory with only firefox open so you can see it does not take much to run out of main memory and start using the swap file for most of the memory work( which is quite a bit slower).