From the bbc site:

"If you've being looking forward to the imminent DVD release of
Doctor Who's most epic classic adventure, The Trial Of A Time Lord,
then you'll have to wait just a little longer.

2entertain have announced that the four-disc set, originally slated
for an August release, will now materialise on 29th September, 2008.
We can't confirm or deny that this is due to meddling by The
Valeyard...
To fill the gap, 2entertain have pulled forward the release of First
Doctor tale The War Machines.

Seen by many as a precursor to the Earthbound UNIT era of Doctor Who,
The War Machines sees William Hartnell battle tank-like robots and a
mad computer living in London's Post Office Tower.

In other DVD news, the cover for the upcoming Fifth Doctor adventure
Four To Doomsday has been released. Follow the link to check it out.

http://www.bbc.co.uk/doctorwho/medialibrary/images/other-
size/fourtodoomsday.jpg"

Source - http://www.bbc.co.uk/doctorwho/s4/news/080807_news_02