Can I use LINQ with databases other than SQL Server?

Yes. DLinq, the database implementation of LINQ, uses ADO.NET for its database connectivity, so in theory, DLinq applications can connect to any database that uses a .NET Data Provider. As you might expect, however, the prerelease code works best with SQL Server 2005. Support for other databases should be available when the product ships.

Will there be a tool to help create the database-object mappings used by DLinq applications?

Yes...