This is the step-by-step process that I went through for each of my months. Each print probably took me a combined 2-3 hours, but I got faster as I learned how to work smarter.
Step 1: Find a backround and models that you would like to use. The better quality and the more of the body, the easier it is to work with.
Step 2: Cut the models out of their picture using magic wand with high tolerance for bigger pieces and polygonal lasso for details. After the bodies are completely cut out, magic wand the bodies, click Apple->Shift->I, and click delete. Tada! The models are cut out of their background. Touch up using polygonal lasso tool.
Step 3: Fill in missing body parts. Examples here. Save as a .psd.
Step 4: Move into Adobe Illustrator. Create a new document for print. File->Place->your .psd.
Step 5: Click “Live Trace” at the top of the screen. I like the preset “Black and White Logo” for the smoothest appearance. If you use this preset, be sure to set its color back to CMYK for ideal printing.
Step 6: Punch in your wallpaper, calendar, and quote, and you’re done! Be sure the colors and quotes match the month :).