This is a bit late, but I thought everyone should be aware that many old Dungeons & Dragons books (and a few newer ones) are available at RPGNow. I recommend checking them out! Some are free. If you have bought older pdf versions from a few years back, you can redownload them. The pdf's have also been cleaned up, so there's no more crappy scans to worry about (which happened to me with a few of the books).
Funny thing is over half of the bestsellers are now D&D stuff, and they've only been available for one day. Moldvay Basic is Number One!
For those worried about it, I've used RPGNow extensively, and I've never had any issues with them (other than when WotC pulled it's pdf's a few years back).