Patrick, you will need to use VBA behind your form (which you probably knew).

Selecting the contact to link top can either be done by populating a
dropdown box with a list of clients, or by selecting the contact from the
folder. You might be better to add a button to the contact form to (add
linked appointment) which would negate the need to find the contact.

Once you have the contact and the new appointment item you can add the
item.companyname, item.businessaddress, item.body fields to the appointment
item body.

How is your VBA?