My friend and I are planning a party for the DH premiere in November.

I literally just found this awesome website with all these different ideas for a Harry Potter party. Some of them may just be right up your alley. Good luck! I generally just dress up and go. This year I'm sitting in the fancy section of my local theater where we can drink alcoholic beverages and I just turned 21! So I can enjoy a Butterbeer while watching Deathly Hallows :D

Link: link

Yeah, My friend and I usually go the opening day. BUT for this my friend, I might get Midnight showing tickets and have a sleepover. We dress up as characters. For OOTP I think I just wore my Gryffendor robes. For HBP I dressed up as Tonks with the Purple and Pink hair and a punkish style outfit. On another note I have been Hermione and Bellatrix for Halloween. I went to the midnight book release for Deathly Hallows. It was so much fun I wish I would have went to the other midnight book releases. I just became a night owl like this past year. This year I will probably go to the cinema as Bellatrix. I will scare people, but whatever.

Why not recreate your fav scene from DH, encorporating old fashioned dressup with modern computerised scenes like they do in the movie, and cool backdrops.