Well, I have no idea as to if Vista has Windows Firewall included, however I assume it does. If it does have Windows Firewall, you most definitely can find it in the, "Control Panel." However, I don't know enough about Vista to tell you for certain how to get there. Most likely you search for it from the start menu.
Have you installed any anti-spyware, anti-virus, or Internet Security utilities when you got your Vista computer? If so, stopping or disabling their monitoring abilities before heading in-game will free up the processor some more and possibly stop the blockage of voice-transmissions. Typically these applications can be found in your Task Tray (bottom right when looking at the desktop) and double-clicking one of their icons brings up a menu with options to temporarily disable protection.