We have a variety of searches here. The generic Yahoo! search can be used for a search local to the web site. There is also a link to Google News and a link to Google Video.
You may want to try variations on the name of a track or sanctioning body, e.g. for ASA, try the fully spelled out name, the abbreviation, and try sticking "Racing" on the end.
You may want to try variations on a track name. For example, you'll find video for Lime Rock Park if you search for "Lime Rock", but won't find much if any if you include "Park". All tracks have pre-filled video search links on their respective pages. The most video seems to be available for Road Courses. Try the Road America search to see an example of why it's worth fooling around with this.