From Apple's web site...
This update includes the previously released DVD or CD Sharing Setup Update 1.0 software to allow the computer it is installed on to act as an optical drive "host" for MacBook Air computers.

For Mac OS X 10.4.11, this update installs:

Migration Assistant 1.0.6
Mac OS X Remote Install 1.1 (located in /Applications/Utilities)
DVD or CD Sharing (located in the Sharing System preferences panel)
For Mac OS X 10.5.5, this update installs:

Migration Assistant 1.2.3
Mac OS X Remote Install 1.1 (located in /Applications/Utilities)
DVD or CD Sharing (located in the Sharing System preferences panel)
To determine the version of an installed application:

Select the application and choose Get Info from the File menu.
Toggle the General Information triangle to see the version information