how can i attach a taxonomy to the users profile?
Users in Drupal 7 are proper entities and fieldable.

Goto Administration » Configuration » People » Account settings » Manage Fields (admin/config/people/accounts/fields)

Add a new Field.  Choose a label, and choose Term Reference as the field type.  Configure as needed.  This should identical for how you do it for a Content Type (ie, a node).

The click on the Manage Fields tab.  Set up the display for how you need it.

Edit you users, and add in some field data.  It will be in the full loaded $user object, and you can use it in Views over Users.