It appears that HD DVD fans are going to have to wait a bit longer for 51GB HD DVD discs. In a recent statement to BetaNews, a Toshiba spokesperson pointed out that only a preliminary version (1.9) of the physical specifications had been approved by the DVD Forum. Also, the company won't be able to determine whether current players will be able to use this "Trip-Layer" format until the final specifications have been approved.
"We understand that the preliminary version (1.9) of the physical specifications for the triple-layer 51 GB HD DVD-ROM disc has been approved," said Toshiba's spokesperson today.

The spokesperson then added that it has not yet been determined whether current HD DVD players or recorders will be able to use the new format, which the headline of an official Toshiba statement given to BetaNews today is now calling "Trip-Layer." "Toshiba will study the performance of current HD DVD player/recorders with the disc after the standard receives final approval by the DVD Forum."
I'd be very surprised if the final specifications were approved this year. Then again, the DVD Forum may push it through to give them the advantage over Blu-ray. If you'd like to read more, the entire article can be found here.