[JohnUlmer]

Here's another way (this tested on OSX 10.6.8):

To show hidden files, Start Property List Editor, then with it open the file /Users/Library/Preferences/com.apple.finder.plist. Look for the key named “AppleShowAllFiles”, and change its value to TRUE. Type Command-S to save the edit. Then restart the finder, either with `killall Finder` in Terminal or by re-launching Finder in the Force-Quit Applications app (Command-Option-Esc).

In my case I must add that Property List Editor made it obvious to me that I had recently fat-fingered this task at the command-line: there was a Key in the plist named “ApplwShowAllFiles”. Oops.

[MikeCohen]

This didn't work for me until I used sudo.

sudo defaults write com.apple.Finder AppleShowAllFiles YES