An Apple tool designed to deliver zero-configuration networking to Windows clients manages to kill off Internet access for Windows Vista Service Pack 2. When using a computer running Apple’s Bonjour service, a default gateway of 0.0.0.0 may be created on your computer. This problem occurs because Bonjour uses logic to add a route to specify a default gateway of 0.0.0.0 which it does not remove. Microsoft emphasized that manually removing route 0.0.0.0 could be nothing more than a temporary solution. While Vista will indeed be able to regain Internet access, the problem could repeat itself.
More info: KB970313