Unless you have created rules to suit your needs,the default settings of Vista firewall only provides inbound protection though a little protection is there by the basic outbound firewall filters...though this will NOT stop any outward bound data being sent if you pick up Malware or a Virus.
By default,Vista's outbound protection is disabled.
Plenty more on Google if you wish to research this.
Though i must add,i am in total control of my Vista machine and the only user,therefore i know exactly whats going on the system and where i decide to surf. I run the system with Vista's own firewall at default settings with UAC disabled.