Fields to become read-only

Hello!
I have to questions which are kind of connected to one another. I am trying to make a text field, which is connected to another text field. If I fill in the first one, the second should appear (this I managed to do), and the date should be generated automatically in the second field the minute I filled out the first text field. After have filled out the text field, and the date appeared in the second one, both fields should become read-only (every time I save it again, the date generates itself again...). This I somehow can't manage. My second question is similar, I have radio buttons, if I push it a text field appears besides it (this is happening right now), after have pushed the button and the date appeared in the text field, it should become read-only (it changes every time I push any radio button). I appreciate every help I can get.
Thank you very much in advance!
Fruszi