many ways you can do this depending on your requirements.
one way could be to hide all the questions that this user does not need to answer (using the SetState script) based on the group membership
have a look at this example form
http://www.perfectforms.com/Documentation/manual/html/fl_required_field_checking_and_fi.htm
although not exactly what you are asking here, it shows the techniques on how to make specific fields on a form 'mandatory' based on conditions, and the 3rd element where a field is 'mandatory' based on the content of a form field could be the one you need, replacing the 'is mandatory' with field state is normal (ie visible) or hidden for your questions