PC-UI screen

Dear CRM gurus,

Can you please explain me:

(1) Using CRM 4.0 can I use PC-UI for CRM sales scenario. If so, how? Can you give me step by step procedures

(2) Does it need any additional software installed?

(3) With just SAP CRM 4.0, can't I work with PC-UI?

(4) What is (is there) the difference between PC-UI and Internet Sales / e-commerce? Are all these same? Why again Portal appears in the SAP's CRM documentation....

Thank you very much, in advance.

Best Regards

Gopala Turaga