I know its late know, but I would reccommoend against using the expanding foam. There are several reasons why pros dont use it in window installations (serviceabilty, mess, etc). Take a putty knife and stuff the perimeter of the window(between vinyl and frame) with fiberglass insulation. Fill the weight pockets as well. This is what should have been done in the first place. I would also reccommend hitting all the other windows. The energy savings you should be getting from your new windows are flowing out right around them.