How to deconstruct a pumpkin

You have to get the skin off and the flesh cooked.

The easiest way is to cut the gourd into chunks and steam it. When cooled the peel can be easily removed.

Roasting takes longer but results in a far more flavorful product. The pumpkin is more concentrated and if it browns it has more depth of flavor as well.

I have sometimes peeled the pumpkin with a peeler before cooking because I didn't want to wait for it to cool (and I'm not a huge fan of handling slimy cooked pumpkin more than I have to.)

After cooking the flesh can be mashed.

Avoid boiling. The flesh will be waterlogged and in order to make it useful for baking it would have to be reduced/settled+drained, etc. Not good eats.

Hmmm. I'm afraid one of my kids' jack-o-lanterns is going to find itself in a pumpkin curry soon.

** Edit **

I should also note that I have never produced cooked pumpkin that was overly similar to canned pumpkin. I haven't tried. The homemade pumpkin is still recognizable as having natural origins. Canned pumpkin has its place, I prefer it in pie for example, but I wouldn't consider canned pumpkin to be the goal.

** Edit part deux **

Derobert has written a beautiful blog post on this subject that puts this answer to shame:
comestible-orange-goo-making-puree-from-fresh-pumpkins

I would suggest cutting the pumpkin into two halves, scooping out the seeds, and putting them (cut face down) into a roasting pan with a cup or so of water. You do not need to get the pumpkin out of its skin at this stage - it's a major hassle. Just cook in the oven at 350F for 90 min. Then remove from the pan. It's now super-easy to scoop the flesh out of the pumpkins, which you can further process in a food processor.

I'll second the suggestion for peeling and roasting - generally what I do is quarter the pumpkin, scoop out the interior (and scrape it a fair bit with a big spoon - the stringy texture of the interior is generally the worst part of homemade pumpkin, IMHO, and you want to get as much of it out as possible), peel the outside, and then dice it into ~1 inch cubes for roasting. It's not especially sensitive to temperature - I usually go about 400 degrees until it's 'done' (soft, dry to the touch, etc.), then let it cool and puree it in the food processor. Unlike Sobachatina, I have to say that I do love fresh pumpkin in pumpkin pie; the taste is distinct (and won't necessarily be what people are used to), but it's so much richer that to my tongue it more than makes up for it.

I would suggest washing the outside, cutting the pumpkin into two halves, scooping out the seeds and putting the halves one at a time, cut side down on a plate or platter. Cook in the microwave, 5 to 10 minutes per pound (depending on your microwave's intrinsic power). The pumpkin is done when the skin is easy to depress from the outside.

Let cool enough to handle easily, then simply scrape the meat from the shell which is tender now. Don't worry if you get some skin: it is edible and probably has good vitamins and mineral. Good thing you washed it before cooking. Use a wand mixer if you have it, otherwise any tool you have to puree the meat. You may need to add a tablespoon of water, maybe even two, but thicker consistency is better for pies.

Store the puree briefly in he refrigerator or put two cups each into quart sized freezer bags, suck most of the air out, and lay flat on a cookie tray in the freezer. I like to leave the top inch of the bag as clean as possible and fold it under the 'pillow' of mashed pumpkin while it freezes which makes using it somewhat easier. We are happy to use these for pie, pudding, soup or bread for as long as a year after freezing.