dropdownlist disable other dropdownlist

A very simple and crude snippet:

<select name="first" id="first" onchange="if(this.value == 'no') document.getElementById('sec').disabled=true; else document.getElementById('sec').disabled=false;">
    <option value="yes">Yes</option>
    <option value="no">No</option>
</select>
<br /><br />
<select name="sec" id="sec">
    <option value="yes">Yes</option>
    <option value="no">No</option>
</select>

I would leave to you the job of putting those bunch of statements in a separate function and changing the way the function is called as per your requirement.

Thank for your help mate.

Problem is that solution is perfect for html form, not asp.net - therefore I cannot use it within <br> and <td> tags in asp form. I also cannot use method onchange, web developer says that it is no supported by dropdownlist. Any ideas how to trick it? Thanks a lot for your time.

Finch

Edit: Here's the code I want to change:

<asp:View ID="View4" runat="server">
<table cellpadding="4" cellspacing="4">
<tr>
<td colspan="2"><b>Section 3 - Health and Safety Policy and Arrangements</b></td>
</tr>
<tr>
<td>3.1 Does your company have a written Health and Safety Policy?</td>
<td><asp:DropDownList ID="HealthPolicy" runat="server" >
<asp:ListItem></asp:ListItem>
<asp:ListItem>No</asp:ListItem>
<asp:ListItem>Yes</asp:ListItem>
</asp:DropDownList>
</td>
</tr>
<tr><td>If yes, please provide us with copy of your health and safety policy. Please go to section 3.3. If No, please answer question 3.2</td></tr>
<tr>
<td>3.2 Does your company employ 5 or persons?</td>
<td><asp:DropDownList ID="Employ5" runat="server" Enabled="False" >
<asp:ListItem></asp:ListItem>
<asp:ListItem>No</asp:ListItem>
<asp:ListItem>Yes</asp:ListItem>
</asp:DropDownList>
</td>
</tr>