Need data access layer for .NET 3.0

Question

Hi,

We are developing a windows application using WinFroms in .NET 3.0.
We want some good data access layer code/information so that it will be supported in .NET 3.0.

In future the client is going to upgrade the .NET Framework version i.e. going to use .NET 4.0. So this data access layer should support the latest Framework of .NET also.

We have heard about NHibernate and LINQ to SQL but not sure how it will work with .NET 4.0 when the Framework will be upgraded. Also not sure how NHibernate will work with Windows Application.

Please provide information and suggestions on this.

Thanks and Regards
Prasad