How i can handle enter key based in textbox focus?

Hi Expert,
My question is better tricky,i know how to handle enter key event in single for textbox in master page. but in my case, i have a text box and button for do the seach and another login user control to do the login.


Then i have write code for trigger the enter key event to every textbox focus. but alwys search button click event is raising. even if focus the login control text box focus.
Here is my code
<SCRIPT type=text/javascript>
function doClick(buttonName,e)
{
//the purpose of this function is to allow the enter key to

//point to the correct button to click.

var key;

if(window.event)
key = window.event.keyCode; //IE

else
key = e.w ...