Pull the photo into Photoshop. I'm not sure you can do this step in a lesser program. I use photoshop and I use some fairly obscure parts of it too.
Step 1 in photoshop: Use the magnetic lasso tool to select the person's face, leave behind their neck, everything below their chin, and the entire background.
Step 3: Create a new file with a black background layer. Copy the selection and paste it into this new file.
Step 4: Reduce the size of the new file to something really small, like 200 by 200 pixels. Save it.
Step 5: Under: Image>Mode>Indexed Color, Select 4 colors. Make one of the colors black, one orange, one yellow and one white. This will serve you well if you are going to show the pumpkin lit from within. If you are going to show the pumpkin in daylight or some similar situation, select a 3 color profile and use white, orange, and black. Play with the colors used as well as the contrast of the image before you convert the colors. Try to come up with something that you will be able to carve.
Step 4: Once you have something that looks good, select all of the contents, paste it into a new file.
Step 5: Enlarge the new file so that it prints the right size for your needs. The reason you worked with the file in such a small size was to get photoshop to keep all of the colors in large zones. The final result should be similar to a paint-by-numbers drawn by a computer in 1983.
Step 6: Print it out.