NOTHING will take your data directly from AS400 and put it into SAP. You need to stage the process. Try to get hold of the Data Conversion made easy book that came out a few years ago.
There are a variety of mapping/data transformation tools out there:
1) Datajunction (may be able to pull the data from AS400 into a format that the SAP system can read easily for the standard load programs).
2) Legacy Migration Workbench (LSMW) - takes flat files and maps them into SAP. (have to download from SAP...free the last time I downloaded it.)
3)
has a product called SIAMEASE that is designed for data migration into SAP.
4) If you can put the data into tab delimitted format, you can use the CATT tool in SAP to load. (it's designed to test your SAP instance - but it acts like a simple Batch load system as well.
In the projects I've been involved with:
From AS400 our programmer did some of the data massage/conversion and put out a master data file that was appropriate for the materials to load via the standard program. We've always staged the data out of AS400, massaged it in MSAccess - put into SAP load friendly format (essentially using VBA) for use of standard load programs, or used CATT or use LSMW.
Good luck