This is very cool. Microsoft have added a "Create Your Own" form to their Add Search Providers page. This means that you can quickly add any site that has a search engine to IE7's search bar.

All you have to do is search for the word 'TEST' (in capitals) on the site you're interested in.

As an example, type in these values and click Install:

URL: http://images.google.com/images?q=TEST
Name: Google Images

Now you have a quick way to search for an image on Google!