Hi.
Kopete and
GAIM can help you achieve your goals, but you may also need to take a look at the proprietary apis for the messenger clients you wish to use e.g. Yahoo, MSN, AOL etc. You may have to join the various developer programs in order to take a look at the api.
P.S. posting in capitals only is regarded as shouting and please don't ask people to reply immediately because everyone is volunteering their personal time.