SAP makes ERP so complicated! It is widely used by those monster (big) enterprises, like Nortel, Lucent, 3 com...It is hard to maintain, difficult to learn, to custmize and to implement. My previous company does middleware and terminal application for SAN/BAAN ERP systems.
Here is a very brief idea of a typical SAP system implementation:
Terminal App <-> middleware <-> customize SAP System (you can think it's a database)
Typical applications are warehouse management systems.