Hi Ravi - in the Procurement Admin pdf there's a section on how to apply Catalog Forms, this is the term used for "bForms" in 9rx.
Catalog forms are associated to catalog items (Part # or Commodity Code) or suppliers and are displayed when users click Add to Cart of an item that is linked to a form through the FormEntry object (there's a csv data load for this). User's have to enter in additional information before proceeding with defining other aspects of the line they're adding.
Catalog forms work the same way as Partial Items as defined through parametric data. The difference is that you can do just about anything with a Catalog Form as you define the class, fields and can write advanced condition logic and fire triggers. Whereas with Partial Items, you need to live within the framework that Ariba provides.
For simple additional information that you just need to go to the supplier to fulfill the order, implement Partial Items using parametric data (it's quick to implement, you can even do it through the Admin UI). For more complex logic, or if you need to report on the additional information, use catalog forms (they're more work to implement, but give you full control).
Ariba provides some sample catalog forms in the Buyer\Server\sample\procure\forms directory
Scott