Script for managing server IDs
Curious,


$("#delivers #servers") does not do what you think it does, $("#delivers,  #servers") might, UPDATE: unless you mean to look for #servers under #delivers in which case you should strive to only have one tag with the #servers id and then go for $("#servers")
I don't understand why you at one point use $(this).val() and at another point $("#delivers #servers").val() if you say that they both point to servers_id
Furthermore, you could simply use var sid = this.value
You are performing many jQuery calls, those could be cached.
Your comments are too much, you don't have to explain every line ;)
On the other hand, what I would really want to know ( the difference between vmtas and o_vmtas is not commented )
vmtas and o_vmtas are terrible names 
Your indenting is confusing
Consider $.empty() over $.html('')


I took some guesses as to what you are trying to and incorporated my feedback into this:

var $dropdown = $('#vmtas')
var $deliverability = $('#o_vmtas')

//Listen to changes in server id
$("#delivers").change(function () {

    //What server id are we dealing with ?
    var sid = this.value;
    //Is it something we can get deliverability info on?
    if ( sid != '0') {
        $.get("/deliverability/get_vmtas/" + sid, function (data) {
            $deliverability.html(data);
            $dropdown.html('');
        });
    }
    else {
        $dropdown.html('&lt;option value="0"&gt;All Classes&lt;/option&gt;');
        $deliverability.html('');
    }
});