Here's one but it's from 2007, so my guess is that some of the details might be out of date.
https://help.sap.com/esoa_docu_print/erp/2005/Docu_ES_ERP_2005_2_EN.pdf
Here's one on how to use the services, it's MII centric but the approach should be applicable for other SAP services too
SAP MII - How to Browse, Configure, Test, and Consume an Enterprise Service
Rgds
Eng Swee