Well, after I installed Windows 2003 Server R2 and wanted to install MSN, I kept on getting this damn error!
So, after trying to figure out a way of getting around that damn installer... I just gave up and desided to install MSN Messenger 7. After I found a link, I downloaded it and installed it. I signed in and it said I have to update to a later version (Current; Windows Live 2008 or 'MSN Messenger 8'). I thought I will never be able to install MSN! So I just did it anyway; hoping it will work...
To my surprise, it did! It updated to the latest version without any problem!
Now I'm happily running Windows Live Messenger without any problems on one of the non-supported OSes.
Download Password (Filebeam): screwmicrosh1t
MSN 7 download: Download details: MSN Messenger 7.0
Mirror (Incase MS deleted it): Filebeam - Free Fast File Hosting