[plug] List of ports - understanding good / bad / necessary services?

[Daniel]

Hello Plug,
new to Nmap I did a scan at tafe and found Timbuktu, tested again and it
didn't show up.  I find reference to it on the net as a Remote access
tool for mac, but I doubt that (there were no Macs there).

Can anyone tell me what Timbuktu service might be in this case and if it
is good/bad/necessary? 

Is there a good net reference that explains the good/bad/necessary of
services & ports? (I've found a few that list the services, but don't
give details on their virtues)

http://muse.linuxmafia.org/nmap-services
http://packetstorm.linuxsecurity.com/trojans/neo-ports.txt
http://www.graffiti.com/services

Thanks very much,
Daniel.