Even if you turn off the firewall, which I don't think you can do, you still have NAT to deal with and that'll prevent you from hosting something unless you move your computer into the router's DMZ or ...

Another fix for AirPort connectivity issues: Turn off Firewall We continue to report significant issues with Airport/wireless connectivity after the update to Mac OS X 10.4.8. MacFixIt reader Ben ...

If your Mac is behind a corporate firewall and is therefore unable to access the CDDB database (which iTunes attempts to connect to whenever there is an active Internet connection and a valid audio CD ...