This is a role-playing site, right? And D&D is one of the better known, more popular roleplaying games out there, right? Well, you can't play if you don't know the rules, but fortunately, most of the essential ones are available for free, thanks to a rare flash of genius on the part of Wizards of the Coast.
You can download them as .txt files here: http://www.wizards.com/default.asp?x=d20/article/srd35
Or read them in html, complete with handy links and other goodies, here: www.d20srd.org