"this application requires the windows installer to run."
I'm running this as user, not root.
If you've installed Outlook, Windows Installer has been installed already.
Chances are, when you run Outlook as root once, this error won't re-occur for you as user.
Background: Under Windows, there are per-user and per-machine installation modes, however, even the per-user installations only work if you're installing as an admin.