It should be at Barnes & Noble and also Amazon.com (
Dennis O'Neil, The DC Comics Guide to Writing Comics; there's also some useful stuff here:
Panel One: Comic Book Scripts by Top Writers). I got mine from the library 'cause I'm a cheapskate like J. Jonah Jameson :) You'll get the most out of O'Neil's book if you've read some comics which illustrate the principles involved, so you might want to also pick up some reprints of one of the better-written titles like Stan Lee's
Spider-Man run, Chris Claremont's
X-Men, Frank Miller's
Batman, Marv Wolfman's
Teen Titans, Alan Moore's
Watchmen, or Neil Gaiman's
Sandman--most of these will also be at Barnes & Noble.
And yeah, feel free to pick my brain for villains--I love plotting deviousness, bwahahaha! :)