Configuration that goes into the script tag.
<asp:textbox runat="server" TextMode="MultiLine" id="Textbox1" Width="350" rows="15" Text="This is some content that will be editable with TinyMCE." />
<tm:TinyMCETextBoxExtender ID="TinyMCETextBoxExtender1"
runat="server"
TargetControlId="content"
/>
And the result. View the source of this page to see how the HTML looks.