If you do the proper pre-production planning, you can do everything you want in Photoshiop. I shoot everything against seemless paper -- choose the color of the paper to match the background replacement image -- then combine everything in Photoshop.
For what it's worth, I created a calendar in 2002 using an Olympus 8080 point and shoot and Photoshop. Check out the calendar and more samples here:
http://www.martygast.com/calendars/satc/
This picture was created using four separate images - model (shot on white seemless), candy box, red hearts and white hearts.
This picture was created using five separate images - model (shot on blue seemless), foreground plant, pool of water, waterfall and the background mist.
