<form name=f>
<input type=checkbox onclick="document.f.b.disabled=false;document.f.b.disabled=false;document.f.c.disabled=false;">a
<input type=checkbox name=b disabled>b
<input type=checkbox name=c disabled>c
</form>
<input type=checkbox onclick="document.f.b.disabled=false;document.f.b.disabled=false;document.f.c.disabled=false;">a
<input type=checkbox name=b disabled>b
<input type=checkbox name=c disabled>c
</form>
<input type=checkbox onclick="checkThis(this)">a
<input type=checkbox name=b disabled>b
<input type=checkbox name=c disabled>c
</form>
<script>
function checkThis(o)
{
if(!o.checked)
{
document.f.b.disabled=true;
document.f.b.disabled=true;
document.f.c.disabled=true;
}
else
{
document.f.b.disabled=false;
document.f.b.disabled=false;
document.f.c.disabled=false;}
}
</script>