On one of the XP threads on this forum, there are instructions for disabling (or enabling) Windows Firewall when it can't be done using the Control Panel applet Windows Firewall. [The Control Panel applet's on and off options are grayed out, and this msg is displayed: "For your security, some settings are controlled by Group Policy".]
The following XP instructions seem to work under Vista, too: http://windowsxp.mvp.../resetfwpol.htm
However, I was still unable to turn off WF until I also went into secpol.msc (Start --> Run --> secpol.msc) and disabled WF in several tabs. Finally, WF is off.