Unlike other similar services, Google Video allows not only viewing video inside client's browser, but also downloading it to the computer and then playing it with Google Video Player. The downloaded video format seems to be "proprietary" (it has the non-standard ".gvi" extension), but it can be easily converted to the common "avi" format with Naevius GVI Converter.

http://www.dvdsoft.us/gvi-converter.htm

http://www.naevius.com/