All colors: A heavy duty (40%) peroxide bleaching, prior to using Manic Panic, is mandatory in order to get the colors to really show up. For those of you in middle america wondering where you can get your hands on said product I recommend goin to Hot Topic (http://www.hottopic.com/) . This is a goth/punk chain that, oddly enough, is located in malls across america.
When bleaching try to achieve a color that is similar to the inside of a banana peel. If you don't bleach and you have dark hair you will just end up with highlights that only show up in bright light. The bleaching process will dry your hair out severly so be sure to use lots of conditioner for at least the next week. In my experience the Manic Panic itself does not damage hair in any noticeable way.
The vampire red color: If you bleach your hair too light you'll end up with a color that is closer to hot pink than what you were expecting the first time. Don't panic. Let it dry and then re-apply another dose. From then on every time you redo the color it will come out a nice vampire red.