Haven't played for ages, but this is good starting point if you're completely new - http://www.wizards.com/dnd/Feature.aspx?x=new/learntoplay
This one is also very useful - http://www.d20srd.org/
You can also find lot of downloadable PDFs on net (wink, wink).
Though, best thing would be to find good DM - D&D is quite complex, so that would help a lot. Plus, make sure you research stuff for a bit, there's lot of people out there passionately hating 4th edition and playing by older rules.
That said, you might want to look in some easier systems for start - I find FUDGE, which is quite light on rules, very easy to understand and get it going - plus you don't need to buy specialized dice if you don't want to, you can easily make them from standard d6 (six-sided dice) http://www.fudgerpg.com/
GURPS is also very good and popular system (original Fallout was to be based on it, but due to some legal issues they had to change it to internally developed SPECIAL which quite heavily borrows from GURPS) http://www.sjgames.com/gurps/
