I found out why I couldn't install MSN Messenger on my tweaked Vista installation, seems like I haven't managed to move the WinSxS folder properly and thus there are problems when I'm trying to install shit. And the only shit I tried to install was Messenger.

Oh well... back to the drawing board, better test it out on a Virtual PC instead of waste my eeePC's SSD lifespan just going through installation again and again and again...