Do you have an established group you're going to join?
If so, they'll pretty much decide this for you. Expect to reference a Player's Handbook or the System Reference Document, but you won't need much else.
If not, and you're likely to be running the game, I strongly recommend you look into some of the simpler systems on the market. The days when D&D was a good choice for a new gamer pretty much died when TSR cut off "Basic" D&D to focus on "Advanced." If you can find a copy, look into Spirit of the Century or Savage Worlds (both much simpler systems that have a lot of good advice for a new game master). Or, if you can find a copy of Basic D&D (either the "Red Box" or the "Rules Cyclopaedia," both out of print from TSR Incorporated), that's a game very friendly to new game masters.
Alternately, if you're at all interested in Star Wars, consider the recently released Star Wars Saga Edition, which is a really excellent, somewhat simplified implementation of the "d20 system" that underlies D&D. It should be easier to pick up, being a simpler game and one for which you have very strong media 'hooks' to grasp concepts with and then explain them to players. It's also widely touted as being a sort of 'testbed' for D&D 4e, so in a certain sense it's a chance to get used to 4e before its release.