When your Apache is configured with suexec enabled, you have to choose either the correct location when installing Mailman (under suexec_docroot) or recompile Apache so suit your installation needs.

I choosed a compromiss:

1. Recompile Apache with --suexec-docroot=/home 2. Install Mailman under /home/mailman

When configuring Mailman, choose --with-cgi-gid=mailman (not the usual group 'www' for virtual hosts)

After installation of Mailman, some permissions have to be altered:

 - $prefix/cgi-bin* should be owned by mailman:mailman
 - $prefix/cgi-bin shouldn't have group-write-access (suexec doesn't like that)
 - disable cgi-scripts' setgid-bit (suexec doesn't like that)

 # chown mailman:mailman $prefix/cgi-bin*
 # chmod g-w $prefix/cgi-bin
 # chmod g-s $prefix/cgi-bin/*

Ok, then you can add specific virtual hosts for list administration:

 <VirtualHost YOUR_IP>
 ServerName      list.somehost.de
 ServerAlias     list.somehost.de
 ...

 SuexecUserGroup mailman mailman <-- this one is important

 #
 # Mailman Sektion
 #
 ScriptAlias     /mailman/       /home/mailman/cgi-bin/
 Alias           /pipermail/     /home/mailman/archives/public/

 <Directory "/home/mailman/archives/public/">
  AddDefaultCharset off
 </Directory>

 </VirtualHost>

It worked fine for me, and I hope it will for others :)