before the voucher expires you must schedule an appointment at a test center (not sure if THE FIRST appointment has to be within the expiration date, but that's not important anyway). Then you can postpone your exam date as often and as long as possible.
How can I have my exam voucher extended past the expiration date? Voucher expiration dates cannot be extended. You must register and take your exam prior to the date printed on this voucher. Neither Prometric, Authorized Prometric Testing Centers, nor Sun Microsystems are responsible for vouchers that are not redeemed by the expiration date. Candidates that chose not to register and take their exam within the one year time frame will not be given an extension.
(bold text by me)
Kai [ February 23, 2007: Message edited by: Kai Witte ]