You could use a Tab Control ( 1 point labels, bo borders, no colors ) with 2 tabs, the second one showing the field.
With 11 an OnObjectModify trigger placed on the radio button will fire a script that will show the second tab ( and so the contained field ).
With 9 ( and 11 ) you could make the radio button itself a button that fires the script.
yes that looks as if it will work fine and is easy to integrate with my existing file.
Many thanks for the quick reply.