Yahoo! How to talk to your kids about the birds and the bees
The most important thing I took away from the video was that your conversations don't need to be scheduled and planned. They are much more comfortable when they are casual and quick. Discussing different aspects of "the talk" don't have to all happen at once. Satisfy your child's simple curiosity and leave it at that. In my opinion, offering too much information only leads to more questions, and they may not be age appropriate.
Best of luck, and remember: children pick up early on how comfortable their parents are talking about the facts of life, so try and make sure it isn't perceived as taboo.