Thanks Vasil! That did it.
As I mentioned earlier, my content page is dynamically loading various user controls into a container control (panel). I couldn't use the following script within this content page because the user control (SearchName), might not have been the one that was loaded at the time,
nameTextBox = $find(
'<%= SearchName.FindControl("NameTextBox").ClientID %>');
An exception error would be thrown.
I couldn't quite figure out how to reference the server controls within the user control that was currently loaded. So I took your suggestion and did the following (I don't know if this was what you intended me to do, or if it's the correct way to do it, but it works),
In the actual user control (SearchName), I added the following markup,
telerik:RadTextBox ID="NameTextBox" runat="server" Width="80px"></telerik:RadTextBox>
"<%= NameTextBox.ClientID %>";
Then in the content page where this user control is dynamically loaded, I added the following global variable,
...and added the following to the pageLoad() function,
nameTextBox = $find(nameIDTextBox);
Now, nameTextBox is pointing to the correct object, and I can assign event handlers (e.g. add_keyPress)...or get the contents of the textbox. Again, not sure if this is the correct way to do this, but...