(by Nassr Ismail <nassr_ismail@yahoo.com> ):

Q1- about buying IPs. If I want to buy a class C IP for example , Do I buy range of IPs (256 in this case) ?
(i.e.  122.152.14.xxx ).

A1 - For a big organization, one usually buys a class (e.g. a range of 256 IPs for Class C). For an individual or a small organization, one may buy a bulk of 8 IPs.

Q2- Where can I buy these IPs ?

A2 - Typically, from ISP