Based on Thias blog instructions on building shairtunes for Mac OS X.

• install XCode using AppStore on Mac OS X 10.7 (a AppleID is needed for that)
• open XCode, in the Preferences “Downloads” click on button to download and install the Command Line Tools
• Download and install Mac Ports (http://macports.org/)
• Open Terminal and type:

$ sudo port install git-core libao p5-io-socket-inet6 p5-libwww-perl p5-crypt-openssl-rsa
$ sudo port install pkgconfig

install shairtunes as a damon:

$ sudo mkdir -p /usr/local/bin/
$ sudo cp hairtunes shairport.pl /usr/local/bin/
$ sudo vi /usr/local/bin/shairport.pl # change the path of cli_hairtunes  /usr/local/bin/hairtunes
$ sudo cp org.mafipulation.shairport.plist Library/LaunchAgents/
$ launchctl load org.mafipulation.shairport.plist
$ launchctl unload org.mafipulation.shairport.plist # (to remove)

Attention:

works only while a user is logged in! (on the login screen there is no shairtunes possible) consider using autologin for this mac (but be aware of the possible security risks!)