Yep, you carve the shadow first, and the truly A-R types would spend a lot of time figuring the best position on the pumpkin to cast the shadow as desired. I tend to slap it on there and hope for the best. :) Then carve the front, stick in your candle, and try to tweak the carving (especially the shadow) so things show well.

This is one of the low-skill crafty sorts of things that I really enjoy doing once in a while. I'd also love to do high-skill crafty sorts of things, but lack the perseverance to learn to do them. <g>