Need a suggestion/help

Friends,
I need to create a usercontrol which is like a drop down but here we should provide a feature where user can select multiple entities(i.e through check box's). That is on click of the drop down, we should have a check box list. I have created what i need exactly but here everything is on server side. please let me know if you guys have come accross like this. Help me to ajaxify all the activities.
 
Thanks,
Yathish 
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