<select size="6" name="select" multiple>
<option value="1">11</option>
<option value="2">22</option>
<option value="3">33</option>
<option value="4">44</option>
<option value="5">55</option>
<option value="6">66</option>
<option value="7">77</option>
</select>
<input type="checkbox" name="dd" value="on" onclick=selAll(this.checked)>
<script>
function selAll(chk){
n=document.all.select.options.length;
if (n>0)
for (i=0;i<n;i++) document.all.select.options[i].selected=chk;
}
</script>
<option value="1">11</option>
<option value="2">22</option>
<option value="3">33</option>
<option value="4">44</option>
<option value="5">55</option>
<option value="6">66</option>
<option value="7">77</option>
</select>
<input type="checkbox" name="dd" value="on" onclick=selAll(this.checked)>
<script>
function selAll(chk){
n=document.all.select.options.length;
if (n>0)
for (i=0;i<n;i++) document.all.select.options[i].selected=chk;
}
</script>
function selAll(chk){
var i=0;while(1)try{document.all.select.options[i++].selected=chk;}catch(e){break;}
}
</script>