Yahoo Messenger 7
Download Yahoo Messenger here
Use the /Q switch in your RunOnceEx.
Example:
REG ADD %KEY%\001 /VE /D "Yahoo Messenger 7" /f REG ADD %KEY%\001 /V 1 /D "%CDROM%\Software\YahooMessenger\YahooMessenger.exe /Q" /f
If you use a different localization and have that one installed, get the web setup, after it finishes downloading and starts installing, browse to %programfiles%\Yahoo!\Installs and take out the setup file. Use switch
setup.exe /S