Is there a way to make my MacBook Pro running Snow Leopard hibernate with a keyboard shortcut?
Option-Command-Eject is the system-standard key to put the machine to sleep.

If you want to do more than sleep, you can use this preference pane to fine-tune the sleep or hibernate behavior: http://www.jinx.de/SmartSleep.html

Edit:

More information about sleep, hibernate, and more on the Mac: http://www.geekguides.co.uk/104/how-to-enable-hibernate-mode-on-a-mac/