Do you have any experience in developing and operating applications with Access 2003 front-end & SQL 2005 Express backend? Did you encounter any problems in accessing and modifying fields having SQL 2005 specific data types, such as varchar(max) and nvarchar(max), through the Access 2003 interface?
They say that Microsoft does not recommend this, see:
http://www.databaseadvisors.com/gazette/sqlexpress.asp