<p>This depends entirely on where you live.<br>
Living on campus, it's actually fairly easy to not have a car (I survived quite happily in Houston without one for 2 years). Houston's lightrail system is fairly convenient for the half-dozen or so places that it actually goes - but it has a stop right beside campus and you can get to a grocery store, downtown, and .... the stadiums? The Rice Village is an easy walk/bike from campus, which has quite a few restaurants/stores.
There are a lot of places in Houston that are really only accessible by car, but enough students have cars that you can almost find someone to drive. (Though to add a note on behalf of those who have cars - if you rely on other people for all of your rides, try to pay them back somehow, since $3 a gallon gas, combined with the cost of the car and parking (which just came out to over $600 for me for next year...eep) can add up.)
Living off campus, it all depends on where you live. If you live 2 miles away right next to a lightrail stop and with an easy bike-route between you and campus, it wouldn't be too bad. If your means of getting to campus consist of riding a bike 2 miles down Main St. everyday, you might want to consider getting a car or finding some other living arrangement.</p>