There are plenty of commercial packages available to do exactly what my system did. Try a Google search for webcam motion detection for example, and you will find lots of links.
For hardware, pretty much any kind of webcam will do. I use a small video camera with composite video output, along with a TV tuner card in my PC to grab the images. You can get that sort of camera for about £50 from placed like Maplin. TV tuner cards are only about £30. Alternatively, you could use a USB or Firewire camera.
The software I use requires a bit more computer knowledge than some other systems. My computer runs the Linux operating system, and on it I run a program called motion (motion.sourceforge.net), which does the motion detection, and saves the captured images. The saved images are uploaded to an FTP server using some simple Python scripts I wrote.
Although this set-up led to the criminal being caught, it didn't prevent him from stealing some very valuable things, which have not been recovered. My recommendation would be to use a camera system like this as a second line of defence after a burglar alarm, rather than as the only defence. I have an alarm now as well as the camera.
Back to the burglar page.