Make the best choice for what you can afford and be aware that it will be out dated as soon as you bring it home. Word processing requires only a basic setup, but graphics and games require much more. Try demoing applications in the lab or at friends' houses first. Other members of your family will also want to use the computer so consider their needs as well. Choose laptop or desktop.
Laptops give portability but cost more.
Desktops do not travel well, but cost less, and hold up longer. Decide which platform, PC or MAC, will be most compatible with your place of work. Buy the fastest modem you can afford. 33.6K is recommend. If your local ISP supports 56K, and you are not planning on moving for a few years, then purchase the 56K modem that they support.