I use Firebug and IE Developer Toolbar all the time to debug tricky CSS problems. But occasionally, a tricky bug comes up that only appears when you go to print the page.>
I use the Adobe PDF virtual printer, because it's the closest thing to a real printer you'd get, without wasting ink and paper.
Anyway, it's recommended to have a separate CSS for prints, with much simpler graphics and less of the images you use just for design purposes.