First: The chances depend on many things: total student throughput in FY08, where you rank when you graduate, what your desires are, needs of the Air Force at the time you graduate, etc...
Second: There will be very few CV-22s in FY08 but you can increase your chances by finishing first in your class, letting your class commander know what your desires are, and having the right attitude.
Good luck and enjoy mother Rucker.