The "Advanced" Firewall in Vista gets the job done. I use it. The main problem with it is that it doesn't alert you when it's blocking an outbound connection. So when a new app needs to communicate you have to deliberately open the firewall control panel & create a rule to allow the program access. So for an advanced user this is annoying but manageable. For a more novice user I'd say go with zonealarm (there's a 64-bit available). I've deployed it to customer PCs and it's pretty easy to work with. It pops up with a little "Allow or Deny" box when it's blocking something.