We have a linked server to a DB2/As400 using an ODBC and can pull data fine.  Never tried a push, but it probably depends on the driver.  We also us an OLE DB driver called HiT to push data to an AS400, but it's also supposed to be able to push to DB2 as well.  Not too expensive if you want to check it out http://www.hitsw.com/

Linda