I have done plenty of integration with SAP in terms of processing IDOCs and I understand some of the business processes in SAP on the manufacturing side - but how can I go beyond that and understand SAP even more.
http://www.sapremotelyaccess.com/ - this site provides SAP on a hard drive, do you think it's legal? I'm guessing not!
As far as integration goes, IDOCs are definitely a good start. You can also look into exposing things from Netweaver by creating web services using the ICF node http://help.sap.com/saphelp_nw70ehp1/Helpdata/EN/55/33a83e37...
Theres also gateway and PI for integrating into SAP.