These formulae provide multiple versions of existing packages.
brew tap homebrew/versions and then
brew install <formula>.
If the formula conflicts with one from mxcl/master or another tap, you can
brew install homebrew/versions/<formula>.
You can also install via URL:
brew install https://raw.github.com/Homebrew/homebrew-versions/master/<formula>.rb
man brew, or the Homebrew wiki.