The key to finding the right model for you is to figure out exactly what you need it for. Will you be using it mainly for surfing the Web or word processing? Do you need it to work from home or mainly to save your MP3s and digital pictures?
Then consider the different facets of computer, starting with its hard drive, memory, and processor. Your hard drive is essentially the brain of your computer, where all of your applications, files, and folders are saved. Your memory, or RAM, involves the -thought processes- of a computer, and gets used whenever you have a program open, such as Word or your Firewall. Your processor essentially does as its name suggests, processing the inner workings of how each program runs.
Some other aspects to consider for your computers are also the ports involved, which can connect your computer to your camera or music player. Many cheap laptop computers today also come with wireless and broadband connectivity.