Trick number one: Tell Windows that Windows Installer is a “safe” service. Get into the command line and run:
REG ADD “HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\SafeBoot\
Minimal\MSIServer” /VE /T REG_SZ /D “Service” net start msiserver
Long, I know, but it’ll list the Windows Installer Service as legitimate for Safe Mode. You can actually do this trick for any service, but don’t overdo it: Safe Mode is supposed to be minimal to make sure Windows can start.
Trick number two: Run SafeMSI.exe (link included below). It’ll start the service in Safe Mode. Wow, that was easy. Bravo to Harry Bates, its author: Download SafeMSI.exe
I like the second trick better because it leaves the Windows Installer service disabled normally, but it lets you run it if you absolutely need to do so in order to uninstall something from within Safe Mode. In the event that Windows Installer was causing the problem that forced you into Safe Mode to begin with (unlikely, but that’s why the service isn’t on the safe list by default), the second trick will still allow Safe Mode to get you going in a minimal configuration.