Blocking IM servers

From: Apu - N (Nahasapeemapetilon@simpsons.net)
Date: 12/07/02 

From: Apu - N <Nahasapeemapetilon@simpsons.net>
Date: Fri, 06 Dec 2002 17:15:50 -0600

Hi,
  This is for a project of mine. We want to block all IM using the
firewall. Where can I get a list of IP addresses or server names of the
major IM services? I googled around for a bit and did not come up with
anything relavant. Any help would be appreciated.
Thanks
/A