Autocomplete using webservice

Hello all - as per my other posts, excuse my ignorance, I am new to this and finding myself quite out of my depth at the moment!
Ok, I have set up a text box with an auto complete extender attached that is populated using a web service, et voila:
<asp:ScriptManager ID="ScriptManager1" runat="server"> <Services> <asp:ServiceReference InlineScript="false" Path="~/GetProd.asmx" /> </Services> </asp:ScriptManager> <asp:TextBox ID="txtProDesSearch" AutoComplete="off" Autocompletetype="Search" runat="server"></asp:TextBox> <cc1:AutoCompleteExtender ID="txtProDesSearch_AutoCompleteExtender" runat="server" DelimiterCharacters="" TargetControlID= ...