Just to be sure, are you using the .NET or the ActiveX version? Because, this is the ActiveX section, but you are referring to the SmartTreeView (from the .NET version).
In case you are using the ActiveX, there is an "Enabled" property on each SmartItem that you can set (True or False).
However, with SmartUI for .NET, you can use the same approach. You can set the "TextBoxTool" to "Enabled = False". You could also call it on the SmartTreeView itself.
Xceed Software Inc.