Ajax tool kit drop down help

[smithsf22]

Hello,
I am new to this and have run into a small problem. I am using the Ajax toolkit with VS 2005 to fill some drop downs through a web service and it works great. All of the cascading drop downs work correctly. The only problem I have is I need to copy the drop downs value from each cascading drop down into a hidden drop down. I have struggled with this for a few days now so if anyone could offer me some advice I would really appreciate it.
Thanks

[Hack]

Can't you just populate the hidden drop down at the same time you populate the visible ones?

[smithsf22]

Thanks for the reply, and that is what i am doing. The hidden drop down is populated at the same time. The problem is I am using a 3rd app, so what i need to do is when the visible drop down is selected I also need to set the hidden drop down with the same value.
The problem I am having is that since I am using 3rd party stuff the html is generated dynamically, so I am unable to just do an onclick event for the drop down that would then set the hidden drop down with javascript.

Thanks again

[JPnyc]

But that's almost the only way to do it. If you can't do it that way, that means on select of the first drop down you have to send a signal back to the server and repopulate the hidden drop-down. This kind of thing is almost always done client-side.

[smithsf22]

Thanks again,
I dont think I have explained it properly. There is no problem populating the hidden drop down. The problem is that when the visible drop down selected value is changed I need to also change the hidden drop down value to match because the third party plug in will only see the hidden drop down value not the visible one.
I am trying right now I have registered a javascript function but it never gets called when the drop down's value is changed like so. I have tried to add an attribute to the ajaxed visable drop down to call the javascript that will set the hidden drop downs value... if that makes any sense.

this.MyDropDownList.Attributes.Add("onchange", "setIndex();");