DB2 (aka iSeries AS400) data sources can be connected via linked server or SSIS.
SSIS is the recommended way of connecting to these types of sources.
Profitbase Studio uses the iSeries AS400 OLEDB provider to connect to a DB2 data source.
OLEDB provider and client tools may be downloaded from here:
http://www-03.ibm.com/systems/power/software/i/access/windows/os.html
A user with read access to the database is necessary. Installation of OLEDB provider and client tools also require a user with permission to do so. Linked Server OLEDB Provider option "Allow inprocess" needs to be checked.
FTP with Service Packs here:
ftp://ftp.software.ibm.com/as400/products/clientaccess/win32/v5r4m0/servicepack/si27741/