I live in the Montrose area of Houston and go to U of H main campus, and you don't necessarily need to buy a car to get from one point to the other. The ride from my house is about 5 miles, but it does take you through the third ward area of Houston - meaning that there aren't very many places to stop/the streets are pretty torn up.
Overall, I'd say that if you live within the 610 loop, you can get to most places around town, as long as you're willing to work for it (and get up early to be there on time!)