This is a standard feature of Firefox. Download it from www.mozilla.org and give it a try.
I remember having read about an IE add-on in a magazine a few weeks ago, but I forgot the details. However, a google search turned up http://www.aimingtech.com/aimatsite/features.htm and
but I don't think these were what I read about. Both however seem to be able to do what you want.
Please share your experiences.
I have seen a tool or tool bar that sits at the bottom of a webpage -- that helps you find a specifc word or term by highlighting each instance on that page. But i can't find it. Will someone please advise?