I would like to have the following:

My site is based around Organic Groups - and in order to start a new group up, the person has to submit a form. Already existing groups have to submit this form periodically as well. Thus, for the group name field, I have to allow them to select from organic groups which already exist, yet if their group does not, I would like this functionality to add a new group.

I would think the way to do this is to create a dummy group and have it so when that specific group is selected, the explain field would appear.

I'm not sure if this is a duplicate of http://drupal.org/node/199287 or not.