Apple has released Bonjour for Windows 1.0.4.
Bonjour, also known as zero-configuration networking, enables automatic discovery of computers, devices, and services on IP networks. Bonjour uses industry standard IP protocols to allow devices to automatically discover each other without the need to enter IP addresses or configure DNS servers.
Bonjour, formerly known as Rendezvous, has been part of Mac OS X since version 10.2 Jaguar, released August 24, 2002. Apple first released Bonjour for Windows in June 2004.
With Bonjour for Windows, you can easily network your Windows computer to an existing network or create instant networks of multiple devices without any additional network configuration.
Bonjour for Windows requires Windows 2000/2003, Windows XP or Windows Vista. Make sure you have the latest Service Pack installed for your computer using Windows Update.
More info and download link (2.1MB) here.