How to extend/modify CRM objects like BP, BP Hierarchy?

Hi All,

I am looking for

<b>Q.1</b> how to extend/modify the structure of CRM Objects like Business Partner (BP), BP Hierarchy, Products, Sales Order, Activities, Quotations, Service Tickets, Order Status? The objects are required to be extended as all fields from Legacy system can not be mapped to existing structure of obejcts.

<b>Q.2</b> Is the extension mechanism same for all above objects or its different?

<b>Q 3.</b> There are standard BAPIs/Function Modules available for extracting data to above object or creating above objects. My question is, can I still use them, if I extend the object structure. Do I need to create custom Function Module?

Please help me getting answers for above questions.

thanks in advance,

KP