You could try highlighting the contact in your contact list and selecting 'View Contacts Info' in the contact menu. There should be a place in there to enter an alias for the contact.
xpander wrote:If you have a vcard in your address book, and it contains their ICQ number, Adium will associate them and display their name instead of their #.
but why isn´t adium just displaying the nickname like it does in the "View info" Dialog?
I don't use ICQ but maybe the numbers are their "Screen Name", the nicknames are their "Alias" and you've set up the contact list to show their "Screen Name"?