However, if you need to make changes you will need to do so by December 31. After that you can not make changes to Part D Prescription plans until Open Enrollment for 2007 begins next November.
You do have until March 3,2007, 1 to make changes to your Part A, B, or C (Managed Care) plans which cover your medical costs of such items as office visits, outpatient services and hospital care.
For more information as well as links to Medicare sites and publications read Medicare Open Enrollment Begins.
Be sure to read about all of the changes for 2007.