According to this report:
http://www.comicmix.com/news/2009/07/25/exclusive-torchwood-picked-up-for-another-season-by-bbc/
Though, obviously, it's hard to tell where they actually take it from here.
Apparently Barrowman has said somewhere today (but I don't have a link for yet) that it may well be 13 episodes.
If I had to guess, I'd expect 13 BBC1 episodes as a reboot, with an all-new (bar Barrowman) cast for this new BBC1 audience it's got.
http://www.comicmix.com/news/2009/07/25/exclusive-torchwood-picked-up-for-another-season-by-bbc/
Though, obviously, it's hard to tell where they actually take it from here.
Apparently Barrowman has said somewhere today (but I don't have a link for yet) that it may well be 13 episodes.
If I had to guess, I'd expect 13 BBC1 episodes as a reboot, with an all-new (bar Barrowman) cast for this new BBC1 audience it's got.