I have installed many of these newer panasonic cameras (higher end ones, but I have installed several of these style cameras as well and they work just dandy!). Built in web server, can be viewed from anywhere in the world if you like. It has a built in PIR sensor that can start/stop recording when it sees motion. It comes with recording software that runs on your PC. If you want a wireless version, it is the BL-C30A instead of the BL-C10A. There are also much higher end systems if you want them, which have external inputs for different types of sensors, but you said "cheap" so this one ought to do the trick nicely!
http://www.shentech.com/blc10a.html
You might want to do a little price shopping, I just found a web site that gave good info so you could see some of the benefits.
If you need any more info, just ask and I will be glad to help.
Also, if you want to play around with one of the high end models via the web (this camera is live at Panasonic headquarters in CT)...
http://p.viewnetcam.com:60001/CgiSta...gle&Language=0