Are you trying to run Visual Studio on Windows Server 2008? I have to wonder why - as the name implies, Windows Server 2008 is an OS optimised and developed for a server - it's not really a development OS... but I can't be of any specfic help I'm afraid, unless you've installed a beta version of the SP. Google it - there are known issues.
Sure.
Installer 4.5 is available from
Download details: Windows Installer 4.5 - first result found by putting "microsoft installer 4.5" into Google....