White smoke makes me think coolant is leaking onto the exhaust, at least that is the first thing that comes to mind. The fact that it stops after the car is warmed up kind of leads me to believe that the head might be warped.
Who replaced the head gasket? Not to question your mechanic skills but I had to ask. Also did the head get sent to a machine shop to make sure that it is not warped?
As for the power steering fluid are you sure that is what it was? Check the PS pump and resevoir for any leaks. Clean off the block and disconnect the belt for the PS pump fire up the car and see if you get the same result.
Just some ideas. Hope they help.