You probably already know that SQL Server 2008 RTM'd (yesterday). You need to be careful when installing SQL Server 2008 if you also have Visual Studio 2008 installed. It all has to do with the version of the framework that each product requires. Denis already blogged about it here: http://sqlblog.com/blogs/denis_gobo/archive/2008/08/07/8261.aspx.
I just found out that the SQL Server 2008 release notes has been updated with some extra information about this. Check it out at:
Read the section below the "Before you install" title. It is worth the 3 minutes it take to read it!!!