"Inline Search is an extremely useful free add-on for Internet Explorer that mimicks Firefox's search behavior i.e. it turns searching into a web page into a non modal research experience coupled with a search as you type facility. It integrates flawlessly into IE (version 5.5 or above), giving it that little extra that makes you a lot more efficient when you are looking for a specific piece of information." (via Core Services)
This add-on is fantastic !
You can download it here.