I agree with those who said that you should find out what your local group plays.
Dungeons and Dragons is the most rewarding hobby I have ever had. I have so many precious memories connected to this game it's silly. There is nothing quite like getting together with a bunch of your comrades, cracking the beers (I find it works best if the DM abstains, lol), and getting into character.
Just find a group and buy the Players Handbook of whatever edition they play to start. If it's 3rd Edition, consider buying the handbook for whatever class you end up wanting to play (Complete Arcane, Complete Divine, etc). If they play in Forgotten Realms, buy that Players book as well. I find it ruins things if all of the PC's have all of the DM content memorized.
Get ready for a new addiction my friend, good luck! =)