I know foreverfallout posted the same thing, but I didn't see it as an attention grabber and I felt that everyone should know how easy it is to obtain this epic helm!
First, you can be lvl 65 at the least to summon the Headless Horseman. Second, take a group to Scarlet Monestary and go to the graveyard (you should see tons of people standing near the entrance). Just walk past the mobs and go outside to the GY and find the pumpkin. Click on the pumpkin and accept the quest..turn around and go to the dirtpile to complete the quest, ultimately summoning the Headless Horseman. You can run it 5 times in an hour, and summon the guy Once a day. You get many other epic items (DPS ring thats really lackluster, but 31 stam and 60 AP might be really nice for most people). Also you get a chance at The Horseman's Helm CHIGGITY CHECK IT YO!