There’s a new SQL book out: “SQL: Access to SQL Server”, by Susan Sales Harkins and Martin W.P. Reid. You can find it at http://www.apress.com. I just got my copy, and it looks great! It focuses on both Jet SQL and T-SQL (SQL Server) and does it in a style that is very accessible.
The book includes tips on using new features in Access XP with SQL Server, but it’s mainly a great reference on using SQL in the Access/SQL Server environment(s).