There have been several topics on this issue already. IIRC, if you're under the hood in VMC then technically you may log the time as PIC since you are "sole manipulator or the controls". However, many airlines will not accept that time since as PIC since you're not the ultimate authority for the operation and safety of the flight...the instructor is (remember, you're under the hood). I seem to remember that you cannot log time in actual IMC as PIC since you are not instrument rated yet. Someone correct me if I'm wrong.