Customer Furbished Material in purchasing

Hi,

We have a scenario wherein the customer sends a part which goes into the BOM to make a finished assembly. How do we raise a PO to the customer for this part with a zero value? I have defined the vendor in the customer master (account control) and vice versa. SAP documents say we need to create a PO for the customer with item category C, but I do not see item category C in purchasing. Any help would be appreciated.

http://help.sap.com/saphelp_dimp50/helpdata/en/16/90713a318db647e10000000a11402f/content.htm

Thanks,

Deepak.