For anyone setting up Mailman on the OpenSolaris distro, this is what I ended up adding to /etc/apache2/2.2/httpd.conf. (Of course don't forget to start the apache service as well: svcadm enable apache22)

ScriptAlias /mailman/ "/usr/local/mailman/cgi-bin/"
Alias  /pipermail/    "/usr/local/mailman/archives/public/"
Alias  /icons/        "/usr/local/mailman/icons/"
<Directory "/usr/local/mailman/archives/public/">
        AddDefaultCharset Off
        Options Indexes FollowSymlinks MultiViews
        AllowOverride None
        Order allow,deny
        Allow from all
</Directory>
<Directory "/usr/local/mailman/icons/">
        Options Indexes FollowSymlinks MultiViews
        AllowOverride None
        Order allow,deny
        Allow from all
</Directory>
<Directory "/usr/local/mailman/cgi-bin/">
        AllowOverride None
        Options None
        Order allow,deny
        Allow from all
</Directory>