Here is a flashing tip from Fine Homebuilding. (Hint: install the window into a flashed opening prior to putting up the plywood siding.)
http://www.taunton.com/finehomebuilding/how-to/qa/window-detailing-for-t-111-siding.aspx
(http://www.taunton.com/CMS/uploadedImages/Images/Homebuilding/QA/hb158QA03-01_lg.jpg)