I tried running VS 2008 SP1 today. I also happened to be running Office and SQL Server. Clearly, that was a mistake as the installer took its requisite hour to install only to tell me it errored. So, I rebooted and tried it again with nothing Microsoft running and it worked fine. I know I'm shocked. One of my biggest annoyances with Microsoft is that many installers require seemingly unrelated applications to be closed. It is one of the reasons I switched to Firefox.
By the way, what is with having to run "SPInstaller.exe"? What happened to good ole' Setup.exe?