Using fresh pumpkin as a substitute for canned
Either boiling or roasting would work, but roasting may be less work (since you don't have to peel and dice the squash).  Roasting may also give you better flavor.

Here is one recipe for homemade pumpkin puree, from Alton Brown, but the basic technique is very simple:


Cut the squash in half and scoop out the seeds and loose pumpkin... erm... guts
Roast the pumpkin, until it is soft, cut side down
Cool
Scoop out the flesh
Puree


Please also see our very own blog entry by Derobert, describing the process in detail.  He recommends a second bake of the puree, to reduce its water content and more closely resemble the canned product.  This will of course also intensify the pumpkin flavor.

No additional spices or flavoring are required; they will typically be added in the recipes wehere you use the pumpkin.