Hi Bertus,
In JavaScript – in ScriptUI, not in InDesign’s dialogs – you can set enable property of control objects to false.
As to Applescript Studio, I think, It’s possible too, but I’m not sure – attributes pane in the Info window has ‘Enabled’ checkbox. I did an interface with radio buttons group (BTW in Applescript Studio it’s called matrix) long ago, but it was quite a hassle. I was doing it by trial-and-error method as couldn’t find an intelligible reference. But the interface came out more attractive, and what was more important to me, Cyrillic characters were fully supported, as opposed to InDesign’s dialogs.
Kasyan