Frazier mentioned something about this to me several weeks ago, but I finally found and installed the U of M library search bar into my Firefox browser. At first glance, it looks like a great project. The search bar is unobtrusive and allows you to search the library catalog without going to the library homepage. You can search by keyword, title, subject, author, or ISBN/ISSN. For my own purposes, I'd like to see a call number search, too, but that doesn't exist at this point.
The LibX extension works with both Internet Explorer and Firefox, and there have also been versions created by a number of other libraries as well - so if you're not at the U, you might be able to find this extension at your own library.
Go to http://www.lib.umn.edu/site/libx.phtml to install the University of Minnesota version.