Extending the Users Panel and Add User screen

Is there a way to extend the Users panel in WordPress 2.7? My site offers paid subscriptions, so I’d like to add subscription status column (right now I have a separate page for this, which is kinda clunky).

Ideally, I would also like to add an extra field to the “Add/Edit User” screen, so I can create new users and set their status from there.

I tried searching for hooks that would allow me to do this, but haven’t found them yet. If they do exist, please point my in the right direction!

thanks!
Jim.