At work on my windows machine I've used Autohotkey to remap the CapsLock key to ESC. I've gotten used to it and on my personal machines (mac) I keep hitting CapsLock out of habit when I want ESC.
How do I do the mapping on the Mac? The keyboard & mouse prefpane has some basic options for the capslock key, but that only lets me reassign it to ctrl, command, or option.