Computer Memory Advisor said..
RAM is “random access memory”. Basically, the more RAM your computer has, the more operations/programs it can run at once. Windows XP recommends a minimum requirement of 128MB (megabytes) of RAM. Other options include 256MB, 512MB, and 1GB (gigabyte, which is 1024 megabytes). Unless you plan on doing any kind of gaming or image processing, 512MB is your best bet. It will allow you to run multiple programs at once, such as word processing, Internet browser and email, without much slowdown at all. If you do plan on doing some higher-end computer work, 1GB of RAM is highly recommended. If you really feel like you won’t be using your computer all that much, or only dealing with one program at a time, 256MB will suit you.
If you are worried about how much RAM you might need in the future, ask if the computer you are interested in has any spare memory slots when you purchase it. You can purchase sticks of memory separately in the future and have them installed to up your ram. For example, if you purchase a computer with 512MB of RAM, and it has an extra slot for memory, you can purchase another 512MB stick of RAM later on, install it, and then you’ll have 1GB of RAM.