While I may suggest a look at GAIM over at http://gaim.sourceforge.net/ , my thought here is that you look for a setting to block all but those messages that are not from your "buddy list."
Bob
hi i have been getting im's on yahoo messenger from a person i do not want. i block them then he creates a new name and continues any way i hate the thing is there a way to disable or remove it
i use internet explorer via dsl sbc yahoo and i have a pc ibm to be exact running windows xp home edition. it starts up every time i change user names too which is annoying when i have to exit the program every time i change user names which is often thanks in advance barbara

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic