Birdcam or Birdhouse Tv
First, you need a birdhouse. You can build your own, but if you're in a hurry you can obtain a pre-assembled wooden birdhouse for just a few dollars at Wal-Mart or Target. When you get it home be sure a cut off the little stick that most commercial birdhouses have under the round opening...it isn't needed by the mother bird, and serves only as a perch for other birds to harass the mother and her babies.
You will need a television camera. Because birdhouses are so dark inside, a black-and-white camera will actually provide better results than a color camera. Tiny B&W TV cameras can be obtained for as little as $13 at companies like Supercircuits. Be sure and buy a matching power supply or battery box when you order the camera. When the camera arrives take it to your nearest Radio Shack and purchase an RCA-RCA extension cord long enough to carry the video signal to inside your house.
Run the camera cables into your house, perhaps to an un-used televison. Hook up a battery for the camera, set the lens focus to about 3 inches below the bottom of the hole in the birdhouse, and wait for the first occupants.