If torchwood is to return, when would this start filming, as it appear JB has signed up tp do desparate Housewifes

http://www.digitalspy.co.uk/ustv/s21...ousewives.html

Well assuming they not annouced the new series yet and they would some prep work I guess JB would be done in the US before TW filming started.

LONG before Torchwood starts filming. His work on Desperate Housewives will be concluded by sometime in May at the absolute latest

I thought maybe. Torchwood is was all but Dead in the UK.
Fox. In the US Says they are doing a Pilot for a US Torchwood and Barrowman would star in it. And I have not heard anything about The BBC renewing (I guess the UK calls it RE-Commision) for another Season/Series of Torchwood.

I read somewhere that RTD will start series 4 filming in january

No - he said things should start moving in January. There's still been no announcement of it being recommissioned.