As far as I know, you cannot, at least, not directly. ADP is specifically
designed as SQL Server/MSDE front end, not anything else. Indirectly, you
can create a linked server (link to SQL Server) from AS400, so that the data
from AS400 is supplied to ADP through SQL Server's link. Note, the linking
is done on SQL Server end, not directly on ADP side. So you still need SQL
Server. Thus, the question become why to do that? You can simply use *.mdb
linking to other type of data source than SQK Server.
If in your ADP app (with data mainly from SQL Server), you need to
occassionally get small amount of data from other source than SQL Server,
you can simply write some VBA code, using ADO Connection/Command/Recordset,
to access data on those sources. Or create linked server on the SQL Server
to get data from there.