It looks like "Ripper" is slated to a be 90-minute show on the BBC, not a full blown spin-off.TV.com is showing "Ripper" to be airing on Jan 1 2008 on the BBC-2, but I don't see it on the BBC site--nor on Anothony Stewart Head's website (http://www.anthonyhead.com/home.html). A long time in the making, but it may not be here just yet.
From the TV.com link:
Rupert "Ripper" Giles spent seven years guiding Buffy, the Vampire Slayer, in her role as the Chosen One. Now his Slayer has changed the world, and Giles must find a new path. This long-awaited spin-off from Buffy the Vampire Slayer follows the adventures of Rupert Giles after the earth-shaking events in Sunnydale.