First, there's the video- it's one of over a dozen, but this is the one that got my attention, because this was **MY** high school. I remember those walls, that parking lot, a few of those police/emt/teachers in the vid. I didn't know going into the video what I was going to be watching, I was just surfing random videos related to my home town.
http://vids.myspace.com/index.cfm?fuseaction=vids.individual&videoid=7780089
Now, here's the page that explains exactly what is going on.
http://www.shatteredlives-montgomerycounty.com/about.htm
I remember staging a VERY WEAK version of this when I was in high school (10 years ago). We pulled kids out of class randomly and made them wear a black shirt with a sign taped to is saying they couldn't speak, they'd died in a drunk driving accident at <insert time here>. It had a visual impact, but not a long lasting one, I'm afraid. I much prefer this program, which I'm sure takes a LOT more work, but I doubt anyone who was involved will ever forget it.
I don't know exactly why I'm sharing, I just felt the overwhelming need to pass the links along.
Wow. I don't remember ever doing anything like this in high school. I bet it makes a huge impression, and as you said, it would be very hard to forget.