That is Working Now!!!
I got that working now. This is the steps I took.
1. created my parent recordset normally e.g SELECT * FROM person_category.
2. created my child recordset, however just the fields I required and applied the CONCAT() function. e.g SELECT people.peopleID, CONCAT (people.firstname, ' ' ,people.lastname) AS fullname, people.email, people.person_category_ID FROM people.
3. Tested both quiries successfully in the recordset dialog box.
4. applied the dynamic dropdown server behaviours. In the "select child text", my recordet set was still not appearing so I just selected any field i.e. firstname, then clicked OK.
5. went into code view in dreamweaver and changed the array from "firstname" to my CONCAT name "fullname".
6. went to tag inspector> behaviors> WA dynamic Dropdowns> populate List from array.
7. tested and it works!!!
Many thanks for your help.