/* This script and many more are available free online at
The JavaScript Source!! http://javascript.internet.com
Created by:  |  */

function changeBox(cbox) {
box = eval(cbox);
box.checked = !box.checked;
}

<form name=demoform> <input type=checkbox name=agreebox> <a href="" onClick="changeBox('document.demoform.agreebox');return false">Clicking this text also checks the box to the left.</a> </form>