From Windows 2000 up to Windows 2008 R2:
During safe mode, the Windows installer service is not started, as a consequence, you cannot use ADD/REMOVE programs applet or MSIEXEC to install or uninstall a MSI package.
To solve this issue:
Copy the free tool safemsi.exe on your computer (safe mode with networking support)
the safemsi.exe tool re-enable the Windows service.
Just after this step, you can use msiexec or add/remove programs applet as usual.