SQL Server 2008 was recently announced for download here. This download is a trial version and will expire in 180 days.
As I mentioned some time ago in this post that in order to use server explorer in VS 2008 with SQL Server 2008, you'll need to download VS 2008 SP1 beta. So you'll need this SP if you want to use the entity framework in VS 2008 with LINQ to SQL.
Refer to my original post if you want to get VS 2008 SP1.
I am currently downloading this RC as I write this.