Windows XP SP2 Opens Door For Everyone
 

As soon as you install SP2 on a Windows XP PC with a certain configuration, your file and printer sharing data are visible worldwide, despite an activated Firewall. This also applies to all other services. The PC only has to provide sharing for an internal local network and connect to the Internet via dial-up or ISDN. Users of DSL services are also affected, if a firewall is not integrated into the DSL modem or a common modem instead of a DSL router is used. Additionally, Internet Connection Sharing of the PC has to be disabled

http://www.pcwelt.de/know-how/extras/103039/

Freaking ridiculous if holds water.

*cough*win2k*cough*

what about if the network is linked to the modem through a linux gateway?

/methinks linux server project just got bumped to #1 priority

no worries if you are using a linux router and have blocked most incoming ports