Yes as Santosh mentioned advanto dynamics crm adapter is the best bet for sap pi. This has inbuilt workbench which has most of the predefined schemas for usage.
Else one more old way I known of is using scribe.
Scribe I had used very long back where in this acts as a layer between pi and crm. In scribe IIS is installed and it acts as MS Message Queues. PI can connect to scribe using JMS adapter as well by using http adapter.
Regards
Senthilprakash