If you buy the pass on site, it is valid for admission for 366 days starting from the date of purchase. If you bought one today, it would expire when the parks close on April 1, 2006 (so 366 days, 367 if it is leap year, LOL).
If you buy the pass online, by telephone or at one of the Disney Stores, you get a voucher. You must exchange the voucher for the actual pass onvce you arrive on site. The actual pass is then good for admission for 366 days starting from the date of purchase.
The discount and perks associated with an AP or PAP are subject to change. Some perks/discounts have a limited duration. Most are good during the calendar year, January 1 - December 31. Usually there is a new list of perks/discounts every January - some stay the same, some change, some are discontinued.
Best wishes -