I would have supposed that installing Office 2003 on Windows Vista would simply work.
My assumption was so terribly wrong. Not soon after starting Setup it throws this error message at me:

Error 1913: Setup cannot update file

C:\WIndows\system32\mapisvc.inf.

Verify that the file exists in your system and that you have

sufficient permissions to update it.

So, oviously an issue with Outlook (mapisvc) registering itself in the system.

Running Setup without installing Outlook was just fine. So was when installing Outlook without MAPI (the "Exchange" stuff...) features.

I hoped it to be simply a file permission issue causing setup to fail on updating mapisvc.inf. Looking at the file permissions showed me this:

C:\Windows\System32>cacls mapisvc.inf

C:\Windows\System32\mapisvc.inf NT SERVICE\TrustedInstaller:(ID)F

                                PREDEFINED\Administrators:(ID)R

                                NT-AUTHORITY\SYSTEM:(ID)R

                                PREDEFINED\USERS:(ID)R

So, my permissions are inadequate? Setup does not account to TrustedInstaller Group?

Fact is: I could not edit the permissions in the first place. It was likely to be some sort of UAC (User Account Control) magic trickery.

So I decided to turn off UAC from control panel, not without needing to reboot the machine first of course. So be it...

This finally enabled me to set the file permissions on mapisvc.inf.

First I re-assigned file ownership from 'SYSTEM' to 'Administrators'. Then I added full access permissions for 'Administrators'.

After going through all these hassles, Setup did finally not complain any more and installed Outlook 2003 with MAPI features successfully.