A small word of warning - if you're playing with the Entity Framework and the designer support inside of Visual Studio 2008 Beta 2 then I think it's probably easier to install SQL 2005 rather than SQL 2008 because, from experience, you might hit some funnies right now in connecting VS to SQL 2008.

The one that hit me first was the dialog that prompts you to build up a connection string. It halts when it spots that you have a version of SQL that it doesn't recognise.

This is possibly more of a VS thing than an EDM Designer thing in that you may be able to just type in a connection string and work your way through the rest of the "Add ADO.NET Entity Model" dialog but, for ease, I retreated back to SQL 2005 to try and drop down the "preview count" for software on my machine.