Default Button as enter

 Hi Guys
I have a search function on my site in the footer, now the user types in the information and clicks the search button. How do i make the default button for the search input box as enter. so a user can enter the information and just hits enter on the keyboard instead of using the clicking the search button. heres my code.
<div id="crack1"><input id="txtFind" value="Search:" runat ="server" /></div> <div id="crack"><a class="specialLink8" href="" runat ="server" id="btnSearch">search</a></div>
 
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