Switch on full view, in the Terminal type:#

$ defaults write com.apple.finder AppleShowAllFiles TRUE
$ killall Finder

Alternatively, edit the Finder's preference file directly. It is in your home folder in Library:Preferences:com.apple.finder.plist

In a Text Edit look for the lines:

AppleShowAllFiles
FALSE

and change FALSE to TRUE

In PropertyListEditor look for 'AppleShowAllFiles' and change the value to TRUE

To revert back, type:#

$ defaults write com.apple.finder AppleShowAllFiles FALSE

$ killall Finder

Unhide a folder#

sudo /Developer/Tools/GetFileInfo var
sudo /Developer/Tools/SetFile -a v var