You just create a linked server using the OLE DB provider for ODBC. You use the DSN that you were using for MS Access (PurchasingPlusODBC)
ODBC is on its way out but can be more reliable for these less well known databases.
Here is some more info on setting up an ODBC linked server:
http://www.experts-exchange.com/Microsoft/Development/MS-SQL-Server/Q_21470542.html
Another issue might be that the SQL Server can;t get to the remote .INI file under the SQL Server service account (because its local system). If the ODBC route doesn;t work let me know and we can pursue that,