Vista includes three firewall profiles: Domain, Private, and Public. A firewall profile stores the configuration information for a specific network environment.
The profile that is active determines the firewall rules that are used to protect your computer. If your computer cannot authenticate with a domain controller using any available interface or if all interfaces do not have their location type set to Private, then the Public firewall profile is set to active.
The profiles themselves are fairly self explanatory. You would use the Domain profile when connecting your computer to a domain, the Private profile when connecting to a private network and the Public profile when connecting to an unsecure, public network such as a wireless network in a coffee shop.