Visual Studio 2008 does not support having both Visual Studio 2008 without a service pack and Visual Studio 2008 with SP1 installed on the same computer. Because certain SQL Server 2008 features install components that are also part of the release version of Visual Studio 2008 SP1, SQL Server 2008 requires Visual Studio 2008 with SP1. If Visual Studio 2008 without a service pack is installed instead, it may not work correctly after you install SQL Server 2008.

More about this in this knowledgebase article
There is also an item on connect submitted by Steve Kass:

So I guess I have to wait till August 11th when VS 2008 goes RTM to install it. I don’t want to install VS 2008 SP1 Beta so close before RTM

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