Installing mailman of Fedora Core 5

[Ignacio Verona]

Hi,

I'm trying to install mailman on a FC5 system, but doing 'yum install 
mailman' returns me a lot of lines like:
[1/1]warning: group mailman does not exist - using root

And after that I'm not able to do anything. 
'/usr/lib/mailman/bin/mmsitepass' returns:
Traceback (most recent call last):
  File "/usr/lib/mailman/bin/mmsitepass", line 45, in ?
    from Mailman import Utils
  File "/usr/lib/mailman/Mailman/Utils.py", line 51, in ?
    from Mailman import mm_cfg
  File "/usr/lib/mailman/Mailman/mm_cfg.py", line 51, in ?
    MAILMAN_GID = grp.getgrnam('mailman')[2]
KeyError: 'getgrnam(): name not found: mailman'

Because neither the 'mailman' user or 'mailman' group does exist. Any 
clue about what happens?

thanks a lot in advance,
Ignacio.