Add "AIM" field to Membership profile?

As part of my membership process I'd like users to provide their AIM screen name, as well as have this field exposed in the Membership profile page. How can I do this?

(*Note that I have a simple plugin installed that changes "AIM" to read "Skype" since I actually need Skype, but for our purposes we can assume it is the "AIM" field)

Thanks in advance.