Rice hulls are the cover for the seeds/grains of rice. They are very dry and and help filter the grain bed (if you do all grain) when you are using a sticky substance like pumpkin to prevent a stuck mash. They kind of remind me of dry pine needles but are wider. Here's a pic.
You can use real pumpkin, I used cans for the ease. I recall reading on this forums last year that a lot of people recommend using Sugar Pie pumpkins rather than the big orange jack-o-lantern style because Sugar Pie are a cooking pumpkin and has better flavor. They are much smaller so you would need more. Brewers on this site have also used butternut squash (after all pumpkin is a squash), and even, believe it or not, sweet potatoes will give you a great "pumpkin" flavor.