Worth repeating from Guy Burstein's blog. I've followed some issues people are having with this on an email list. VS2008 SP1 will release "in about a week from now", or sooner, or later, but it is very close. So hang in there.

Certain SQL Server 2008 features install components that are also part of the release version of Visual Studio 2008 SP1. So, if Visual Studio 2008 without the service pack is installed on your machine, you cannot install SQL Server 2008. If you try to install, you will ran into the following error:

Rule "Previous releases of Microsoft Visual Studio 2008" failed.

A previous release of Microsoft Visual Studio 2008 is installed on this computer. Upgrade Microsoft Visual Studio 2008 to the SP1 before installing SQL Server 2008.

In case you are wondering, Visual Studio 2008 SP1 should be expected about a week from now, so you don't have to wait too much.