Try right Clicking on the program and choose "Run as Adminastrator" Then See
if it will install without errors.
also i found this link but it not for vista but may provide some clues.
http://support.microsoft.com/kb/834484
"seb" <seb@discussions.microsoft.com> wrote in message
news:276E219B-E6B7-4A14-B0A7-80B229B783DE@microsoft.com...
> hi, i just bought a new computer with windows vista.
> im trying to install msn messenger live 8.0 and the error code 1603 always
> cancel the installation.
>
> what can i do? how can i install messenger without any problems?
>
> help me
>
> Seb