I would tell veryone who wants an old school feel D&D game and doesn't have any of the old books, this update is outstanding. Its the full version and its free.
http://www.rpgnow.com/product_info.php?products_id=64331There's a full art version and its $5.00. Well worth it. Want to add all the AD&D goodness from the old days, add the Advanced Companion. Its free for the full version, no art, or a pittance for a full art version. No retro clone of D&D does it better. This is all we Roleplay with for D&D now, and I still have all my old books from when they were bought in the 80's.
and if you remeber Gamma World they have a free version called Mutant Future.
these are full games. Incredible value. But be careful you'll get hooked on the simplicity and fun of playing old school sand box style RPGing.
If MMORPG's like World of Warcraft are your cup of tea, you may not like the style of these games as they are based around the originals of the genre and the hobby. 4e may be a better choice.