SPOILERS AHEAD!!!
I have a working draft that's about 3 hrs 40 min long... I'll try to trim it down by a couple more minutes but I think it's found about the right length. The only "tampering" that I did with the footage is near the end (Episode 21) -- I left out the Rack character entirely (I felt that Tara leaving Willow was incentive enough for her to stop using magic), so the only way I could think of getting her into the Magic Box was to create my own teleporting effect, with lightning that ends up hitting Dawn, which explains why she collapses. I've uploaded an XviD clip showing that effect at http://rapidshare.com/files/12283107/Willow.avi.
I titled the movie "Buffy the Vampire Slayer: Back from the Grave". Feel free to suggest anything better.