assginment of services to service type

When creating an order with service type ABCDE as item, item not automatically appearing on order. The service type should automatically map to item as other pm service types work.

For vehicle some service is due on 1st Nov 2009 and the service which needs to be done is ABCDE

when we create an RO for this service type and if service date is DUE then line items for the service are get automatically added as line items to RO

I want to know where is this assginment of services to service type

Thanks & Regards

Vishal