If you are thinking about a desktop, look for a system that is comparable to (or better than) the Dell Optiplex 9010 example system (see PDF below). You will want at least 4GB of RAM, an add-in video card, and a good sized monitor. The monitor's size depends on what you like or have room for on your desk, but most people seem happy with something in the 20" to 22" range. Whatever the size, you want the text and images to be sharp and clear. Remember, you may spend quite a bit of time staring at it so you want it to be easy to read.
A three-year on-site warranty is included in the example system, which means Dell will send someone to your dorm or apartment to fix your computer. All the standard configurations come with this warranty. If you configure a system from the full catalogue, you have a choice in the length of the warranty. When deciding what length of warranty to purchase, try to think about how long you intend to keep the computer. Desktops tend to have a life span of three to four years.