You can use a text field in a form to display messages. You can change this text in the text field when a user clicks a button. You can do this either with a single-line or a multi-line text field.
example:
To Set Text
1. Make your form with a text field in it.
2. In the Behaviors panel, select a browser (3.0 and later).
3. In the Document window,
select an object (a, body, img, select)
4. In the Behaviors panel, add the action Set Text>Set Text of Text Field.
5. In the dialog box, your text field name should be listed. Type in the new
text that you will want to appear.
6. Click o.k.
9. In the Behaviors panel, select an event (onLoad, onClick, onMouseOver).
10. Check it in a browser.