I just found out today that kopete didn't send the buddy icon from my global identity properly. Messenger users in windows didnt see the icon, but other kopete users did. Seems a bit strange, but the problem was solved by setting the buddy icon in the settings of my messenger account. So problem solved, but there is some kind of bug related to kopete's global identity.
Im using Kopete 0.11.1 on my great Kubuntu 6.06 box