The MSDN forums for data access have been restructured a little.

Entity Framework & LINQ to Entities questions:

The one which has always been under "MSDN Forums » Visual Studio 2008 (Pre-release) » ADO.NET (Pre-release)" has been renamed to MSDN Forums » Visual Studio 2008 (Pre-release) » ADO.NET Entity Framework and LINQ to Entities (Pre-release). It's still pre-release, of course.

LINQ (Released)

While there is still a general LINQ forum under MSDN Forums » Visual Studio 2008 (Pre-release) » LINQ Project General  (Yes, under Pre-Release. I imagine they don't want to lose the content or confuse people by moving the forum), the LINQ "flavors" have now been split up and are in the "Data Platform Development" section.

MSDN Forums » Data Platform Development » LINQ to SQL  
MSDN Forums » Data Platform Development » ADO.NET DataSet (This includes LINQ to DataSet)
MSDN Forums » Data Platform Development » XML and the .NET Framework   (This includes LINQ to XML)
 
Regular ADO.NET (aka "Classic")

1) The above linked ADO.NET DataSet forum is the place to go for all things DataSet.
2) MSDN Forums » Data Platform Development » ADO.NET Data Providers  
"Data platform development using classic ADO.NET (v 1.1 and 2.0) and System.Data namespace."