This is not a vista issue this is an IE / MSN Messanger issue.
Besides, you said the OS / IE security didn't install anything, and if you had decent malware/AV installed (which you said you didn't have any) , even if you accidently had OK'd the install of the component, the AV would have blocked the install, well that's what heppens with Sophos if I click to install a baddie.
All in all I love Vista over all versions of windows , it is super fast, looks sleek, i hate having to boot back to XP to run a certian program or game.
And what really annoys me is Adobe & Sun still haven't released a Vista x64 Flash or Java plugin, how lame is that!
I'm still having to open IE 32bit , it's insulting my PC!
"In complete darkness we are all the same, only our knowledge and wisdom separates us, don't let your eyes deceive you.