morkhans is right, using FreeBSD 4 is a bad idea, its ancient.
I haven't been using FreeBSD for a long time, but something like this might do the trick, or at least get you going in the right direction. :erm:
Then edit /usr/local/etc/sarg/sarge.conf and change it to fit your needs and run sarg as root from the cli.
Hope that help :/
I forgot the make install part, not that it will be used anyways...
I normally use CentOS for client firewalls and proxy servers. I don't use all these pre built stuff like ipcop and pfsesnse and all those 'solutions', instead I prefer to use the configs I have built up over the years for iptables filtering, squid etc.
I would suggest to get someone who knows what they are doing to assist you in reinstalling the firewall with a proper OS (FreeBSD is a proper OS but has to be kept current and updated like most other OS's out there).
Note, like morkhans said, ntop and sarg arn't nearly the same thing. sarg is a tool that reports on browsing and works with squid proxy server, ntop is a network traffic analizer.