You didn’t say much about the database but let’s assume it’s AS/400 DB2. You have many options, even if you are using Oracle, MySQL etc..
If DB2 you can use DB2 Connect, it requires a separate license if not already owned.
You can use SQL Server DTS on a PC as a go between.
JDBC or ODBC using home-grown Queries.
You can crate a DB2 Staging DB on the “other platform (also not mentioned) using Federated Database.
You can use High-Speed Unload/Load.
You can EXPORT AS Delimited and Import.
The correct solution depends on the needs, whether Batch or Realtime is preferred.
Another convenience is MQ Series and/or WebShere or BEAs WebLogic.
StartGoogling, write down the requirements and row sizes and number of tables and we can better determine a viable solution, of which there are many.
– Corey from Falls Church