You may want an "other" option while creating radio buttons and check boxes for your form. Simply add an option by editing the target form element, put the text "{OTHER|*number*}" into the option value. The number indicates the size of the input text box that should be generated for the "other" option.

A radio button that has two selectable options and an "other" option with a 25-characters-with input text box.

The result.
The term "Other: " can also be changed by modifying the language file "main.php" under the directory "path-to-liaise/language/your-language".
