Converting a combobox into a textbox at runtime

You can use javascript & for this javascript is the best.
Example:

<asp:LinkButton ID="lbUploadOrThanks" runat="server" OnClientClick="return EnabledFalse()==true ? true : false;"></asp:LinkButton>

<div id="divComboBox">
//put here your combobox
</div>
<div id="divTextBox" style="display:none;">
//put here your textbox
</div>

Javascript:
var J = jQuery.noConflict();

function EnabledFalse() {
J("#divTextBox").show();
J("#divComboBox").hide();
return false;
}