Here is another one:
http://hometown.aol.com/mayassites/whelping/
These sites will help you with understanding pregnancy, what to expect, whelping, and puppy development.
There is such a thing as false pregnancy in dogs. They can also be re-absorbed. Wait another 2 weeks. If you don't see ANYTHING then, there may be something else going on. When they are in heat, their vulva swells a lot, then the swelling goes down. When they get pregnant the vulva doesn't go back to its original size before coming into heat.
I do hope this has been helpful. I'd highly suggest reading over and over and learning as much as you can before the pups come. There is aslo a wonderful Knox gelatin receipe on here for post whelping. You can find that in the "search" option above in the darker blue bar.