<script  runat="server">
Sub choose_image(Sender As Object, e As EventArgs)
   image1.Src = select1.Value
End Sub
</script>

<html>
<body>

<form runat="server">
<select id="select1" runat="server">
   <option value="/i/eg_smile.gif">ЦÁ³</option>
   <option value="/i/eg_bulbon.gif">µÆÅÝ</option>
   <option value="/i/eg_mouse.jpg">Êó±ê</option>
</select>
<input type="submit" runat="server" value="ÏÔʾͼÏñ"
OnServerClick="choose_image">
<br /><br />
<img id="image1" src="/i/eg_smile.gif" runat="server" />
</form>

</body>
</html>