BuddyPress.org

Thanks guys, both of you have been a real help … I managed to figure it out
My solution was following…
In my template I used a function bp_activity_user_id() which echoed user ID , but instead of ID I needed username or displayname . So in bp-activity-templatetags.php I edited the line 380
from this:
return apply_filters( ‘bp_get_activity_user_id’, $activities_template->activity->user_id );
to this:
return apply_filters( ‘bp_get_activity_user_id’, $activities_template->activity->display_name );

You can see it in action here: http://www.fotografija.ba/slike/?afilter=album

thanks again