[iTunes] Re: Deauthorizing Computers

[Jane Lee]

One of my friends had a problem where he bought music from the iTunes 
Music Store then got four motherboard replacements.  Needless to say, 
he authorized the same computer four times and could not deauthorize it 
himself before sending it to AppleCare for a motherboard replacement.
http://www.apple.com/support/itunes/authorization.html
is the address you need.  For future reference, that is.  Hopefully you 
have solved your problem.

Sincerely,
Jane