Hi,
As has been stated elsewhere on this forum Debian (the base of AV Linux) now has a choice of JACK 1 or JACK 2 in the Sid repositories, this change will find it’s way into Debian Testing and therefore into the next Debian 6.0 Stable in the near future. As of AV Linux 4.0 20100706, AV Linux comes with JACK 1 as default due to it’s better compliance with both various software and hardware combinations. AV Linux Ardour packages which are built from Debian GIT are built against JACK 1 so if you are using AV Linux you may need to grab the appropriate JACK from Debian Sid to use and install the latest Ardour packages at the current time.
Just passing this along to clear up any confusion.