<body>
<input name="checkbox" type="checkbox" value="checkbox">
<input name="clickme" type="button" value="clickme" onclick="javascript:document.all.checkbox.checked=true">
</body>
<input name="checkbox" type="checkbox" value="checkbox">
<input name="clickme" type="button" value="clickme" onclick="javascript:document.all.checkbox.checked=true">
</body>
document.all.chkbox.checked=false;