Getting extra information from form

Hi,

I would like to use two input forms to load data into the database. The first form is a generic sign-up for with the usual fields. The second form contains all these fields plus 6 other fields. I could keep these forms on separate pages or display the extra fields when one of the original sign-up fields have a specific value. One form is for a member sign-up and the other one is to capture additional information for volunteers.

Reading through the forums I saw instructions to show field or not in the fields loop but this was for a list. I hope something similar can be done in displaying fields for the input form.