Uh, you can attach a special google search to your web page for free and it will ONLY search items on your web site. That's the closest thing I can think of off-hand. Otherwise, you might be able to just search for a free search utility javascript or somethin. I've never really used those scripts, so I couldn't say for sure.
Try the google thing though...
http://www.google.com/services/free.html
I think that's the same think that fark is using on their page...