Use User Types . Here is a quote about it (from the module project page):
... gives you the ability to create user profiles for specific types of users. To do this, the main profile module must be enabled. It allows you to determine for which profiles the field will be active. For example: if we need a field in which you can enter your favorite group, you will create this field, and at the bottom you can choose for which types of users (which you defined earlier in admin / user / user_types) this field will be active using the checkboxes . It is so simple. It is also possible to automatically assign a role to each type of user.
It is important . This module uses theme redefinition to hide categories of profiles that are empty for the associated user type identifier. Be sure to check out the documentation to copy the PHP fragment into the template.php template.
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