FileMaker can perform ODBC imports from other software providing you have the correct driver from the software manufacturer of the source of the data (AS400). You can setup your ODBC Data source in the FileMaker file if you wanted to script an ODBC Import.
That said, you cannot relate that ODBC Data source to your FileMaker tables unless it is one of the supported External SQL sources. The ESS feature allows you to create relationships and pull live data from a number of SQL sources, and you can find more information on that here: link
In short, you cannot relate an AS400 data source to a FileMaker table. For more information about ODBC you can visit: link
If I have misunderstood your situation, or you have further questions please feel free to ask away :)
Thanks for the reply.. yes it solves the problem. I managed to after some googleing to get to the same conclusion yesterday.
So I have to make do with the import only.