By default, many of OS X’s files and folders – especially Unix-only folders, such as ‘/usr,’ ‘/etc,’ and ‘/bin’ – are hidden from view in the Finder. But you can change the default, so that you always see these files and folders, by typing this command in Terminal (/Applications/Utilities): defaults write com.apple.Finder AppleShowAllFiles YES
After you press Return and restart the Finder (hold down the Alt key and then click and hold on the Finder icon in the Dock), you should be able to see every file and folder on your Mac. (You can reverse the effect by changing the YES to NO and again restarting the Finder.)
If you don’t want to see the items all the time, Snow Leopard offers a new way to see them temporarily, but only in Open and Save dialog boxes: In one of those dialog boxes press c-Shift-full stop (.). This command is a toggle; to hide the hidden files again, press c-Shift-full stop again.