<form name=f>
<select name=s onchange="alert(this.value)">
<option value="aa">aa</option>
</selct>
<input type=button onclick="a()" value=add>
</form>
<script language=VBScript>
Dim b
Dim i
i=0
function a()
set b=document.f.s
b.options.length = b.options.length + 1
b.options(b.options.length-1).text = "item"+Cstr(i)
b.options(b.options.length-1).value = "value"+Cstr(i)
i = i + 1
end function
</script>