Possible to run scripts on sleep and wake?

Question

MacBook Pro 2010 running OS X Lion.

Is it possible to run scripts on sleep and wake events?

My specific application is that I've got Dropbox-synced Truecrypt volumes that I regularly use on both my MacBook and iMac. I rarely shut down my MBP since closing the lid is much faster and easier, but this means that I have to remember to dismount my Truecrypt volumes and let them sync back up before closing my MBP. It's trivial enough to script mounting/dismounting of them, but I'd like to go a step further and have these scripts run automatically.