Tiny Firewall 64 (beta)
So you have installed 64-bit Windows XP x64 on your AMD64 machine and now you are searching for a good 64-bit firewall to go along. If this is the case, take a look at Tiny Firewall 64. As they say, it is a native 64-bit version of Tiny Firewall 2005. You can download a public beta version from this page. The final version is expected sometime in May 2005.