You will either fly into Houston Hobby or International airports. Both are pretty good. Hobby has a contract with Southwest Airlines, and they are almost always the cheapest (if they are contracted with a certain airport). Both are relatively convenient to the city, Hobby to the south, Intl. to the north.
Dear God, the only thing I can say about getting around in Houston is, 'Pack your Valium and leave early.' Houston traffic sucks. It might have the worst traffic of any city I have ever been in.
There are two major Airports in Houston located at opposite ends of the city. If your passing through and be sure your connecting plan is our of the same airport DO NOT TRY TO FLY OUT THE OTHER!
You must have a car. Unfortunately the city public transportation sucks.
There are two major airports, IAH and Hobby. IAH is about 30 minutes north of town (depending on traffic). Hobby is about 30 minutes south of town toward NASA.
You really need a car to get around to all the cool stuff
Hobby Airport is on the south side of Houston just off of Highway 45. It is quite a bit smaller than Bush Intercontinental but is always very busy. It is a major hub for Southwest Airlines.
Intercontinental airport is too far from downtown, and is a pain to navigate. Fly into Houston Hobby if at all possible. This will put you right downtown.