For a great Supernatural/Harry Potter story check out The Art of Survival by gbholderness at Twisting the Hellmouth (www.tthfanfic.com) It's also at fanfiction.net under the name redbanker. Dumbledore hires the three Winchesters as the new DADA teachers. The hunters put their new students under a vigorous physical training regimen, something none of the magic users are used to.