ChshreCat has good info on the pumpkin and as he stated, pumpkin does require mashing.
Most that I have spoken to that mash with pumpkin say that it isn't really worth the extra effort and hassle it can provide. Yes, in order to convert the starches in the pumpkin you would need to mash it, however, I'm trying to get the flavor and aroma from it.
I have done a little research here on HBT and spoken to a few people, and from what I understand, pumpkin imparts little flavor to the beer. Most of what people taste and describe as pumpkin flavor are the spices that are used.
I will be brewing my first pumpkin beer tomorrow (Tuesday 21st of July), and I will just be using 4 cans of organic pumpkin puree that I will caramelize in the oven @ 350° for about an hour (or until I see the caramelization begin) and add that to the boil for the full 60 minutes. I will add my spices @ 10 minutes and allow to steep for 5 more after flameout.
I will make sure to get all of the pumpkin and break into the fermenter, I understand this will help with flavoring.
Check these two recipes out maybe they will halp you to make a decision.
http://www.homebrewtalk.com/f76/richards-pumpkin-ale-23489/
http://www.homebrewtalk.com/f76/thunderstruck-pumpkin-ale-ag-extract-versions-26699/
Good Luck!
