<script> function checkall(formname,checkname,thestate){ var el_collection=eval("document.forms."+formname+"."+checkname) for (c=0;c<el_collection.length;c++) el_collection[c].checked=thestate } </script>

<form name="test"> <input type="checkbox" name="v1"> Peter<br> <input type="checkbox" name="v1"> Jane<br> <input type="checkbox" name="v1"> George<br> </form>

<a href="javascript:checkall('test','v1',true)">เลือกทั้งหมด</a> <a href="javascript:checkall('test','v1',false)">ยกเลิกทั้งหมด</a>