Want to Group names in To: Address List

Exchange 2000 running on 2003 server. We just acquired another company and want those users in our address list but we would like them to be grouped together some way so it is easier to find one individual in that company. We all have the same domain addresses. I have put a letter in front of their display name to keep them together but surely there is a better way. We are only talking about 8 or 10 out of a total of 50 or so. Any help would be appreciated.