It is well-known that MS Access applications (MDBs) using SQL Server backends have trouble with certain data types. For example,
At work, we have the same setup as well (Access 2003 frontend, SQL Server 2005 backend) and we did exactly what you are asking about:
We had SQL Server tables with text/ntext columns, and we changed them to varchar(max)/nvarchar(max).
We didn't experience any problems at all, if I remember it correctly we didn't even have to re-link the tables in Access...it just worked.