Either way, you'll get where you're going. Shoot for the minimum configuration mentioned above. And try to stick to established computer stores that offer warranties. A big risk in buying from an individual is that you'll overpay. The latter can be used to add a printer, scanner, camera or other peripheral.
Laptops come with similar processors, memory, modems and hard drives.
Screens and keyboards will vary in size and quality. Pointing devices will vary, too, with some offering touchpads, some eraser-head pointing sticks and some standard mice. With some laptops, CD-ROM drives are extra, so watch out for that. You'll also want to consider battery life, weight and whether the device can be connected to a standard monitor when the user gets home or back to the dorm room. How much you spend will depend on many different things, not the least of which is brand name.