2012 Requires Windows Vista, Server 2008 or Seven.

2011 Requires Windows XP, Server 2003.

download

Setup switches are documented here

package xml, soon...

1. Download the INSTALL_MESSENGER.EXE file from http://messenger.msn.com
2. Extract the .msi files with the /c option (INSTALL_MESSENGER.EXE /c) to your package directory.
3. Add the following .xml to your packages:

<package
  id="livemessenger"
  name="Windows Live Messenger 8.0"
  revision="80081200"
  priority="10">

<check type="uninstall" condition="exists" path="Windows Live Messenger" />

<install cmd='msiexec /q /i "%SOFTWARE%\Messenger\msnmsgs.msi"'>
 <exit code="0" />
 <exit code="3010" reboot="true" />
</install>

<remove cmd='MsiExec.exe /q /x{5BF18226-EB81-40FD-A61C-835DACFA0E89}' />

<upgrade cmd='msiexec /q /i "%SOFTWARE%\Messenger\msnmsgs.msi"'>
 <exit code="0" />
 <exit code="3010" reboot="true" />
</upgrade>

</package>

The revision field corresponds to the Messenger version, so for Build 8.0.0812.00 it's 80081200. It's easy to follow new versions with this revision scheme.

With version 8.5 you have to install MSN via the Microsoft Live Installer. Install Messenger on a machine and the MSI will be located in
C:\Program Files\Common Files\WindowsLiveInstaller\MsiSources
File name: Install_{508CE775-4BA4-4748-82DF-FE28DA9F03B0}.msi

Use this file to deploy to the other machines

Note: The directory and file is marked as a system and hidden file, so you have to apply the appropriate folder options to see it.