Option onClick in Internet Explorer

In a page that I am working on right now I have this problem:

I have a dropdown menu using select. This menu has two options. What I want to happen is that when I click the first option another dropdown menu (let us call it B), is disabled. And when I click the second option, menu B is enabled. I've tried to solve it this way:

Code: [ Download ] [ Select ]  [ Line Numbers Off ]

<select name='Type'>
<option onClick='dm();' onSelect='dm();' value='DM'>Option 1</option>
<option onClick='rm();' onSelect='rm();' value='RM'>Option 2 </option>
</select>

1. <select name='Type'>
2. <option onClick='dm();' onSelect='dm();' value='DM'>Option 1</option>
3. <option onClick='rm();' onSelect='rm();' value='RM'>Option 2 </option>
4. </select>

(As you can see, I've defined both onClick and onSelect trying to make it work).

The javascript code is in a file called util.js. This is the code:

Code: [ Download ] [ Select ]  [ Line Numbers Off ]

function dm(){
    alert("OK");
    document.newMalForm.menuB.disabled="disabled";
    return;
}

function rm(){
    alert("OK");
    document.newMalForm.menuB.disabled=false;
    return;
}

1. function dm(){
2.     alert("OK");
3.     document.newMalForm.menuB.disabled="disabled";
4.     return;
5. }
6. function rm(){
7.     alert("OK");
8.     document.newMalForm.menuB.disabled=false;
9.     return;
10. }

The javascript file is included using this tag:

Code: [ Download ] [ Select ]

<script type='text/javascript' src='util.js' language='JavaScript'></script>

Now, this works in firefox but not in IE. In fact, IE doesn't even run the functions as the alert (called in the javascript file) isn't shown when I click the menu options. What is the problem?

EDIT: The alert only exists in debug purpose. And I also wanted to say that this is my first post in this forum!

More editing, to clarify: newMalForm is the form that contains both of the dropdown menus.