In almost all organsiations running SAP and Microsoft this is one of the most discussed topics : integration / interoperability of SAP (Portal) and MOSS 2007.
The attached zipfile contains a flash movie explaining all the ins and outs. Very helpfull.
This overview animation explains options and possibilities as well as limitations in the combination of SharePoint 2007 and SAP NetWeaver.
Download: SAP MOSS Interop Animation ZIP