Exchange 2007 Agent installation fails with App Log Error: Source - MSIInstaller, Event ID 1033, Error Status 1603
This MSI error is caused by the .MSI file being run prior to the setup.exe.
Re-name the install Shield folder under:
C:\Program Files (x86)\Common Files\InstallShield
Then re-run the setup.exe.
The InstallShield folder will get re-created during the re-installation.