The dab.conf file of debian-5.0-joomla in dab-pve-appliances_2009-12-22.tar.gz has the commented out Mirror line uncommented (red bold in quote below) now. What difference does it make?
Suite: lenny
CacheDir: ../cache
#Source: http://ftp.debian.org/debian SUITE main contrib
#Source: http://security.debian.org SUITE updates/main updates/contrib
Mirror: http://ftp.debian.org/debian => ftp://mirror/debian
Architecture: i386
Name: joomla
Version: 1.5.10-1
Section: www
Maintainer: Proxmox Support Team <support@proxmox.com>
Infopage: http://pve.proxmox.com/wiki/Joomla!
ManageUrl: http://__IPADDRESS__/
Description: Joomla! Content Management
Joomla! is one of the most powerful Open Source Content Management
Systems on the planet. It is used all over the world for everything from
simple websites to complex corporate applications. Joomla! is easy to
install, simple to manage, and reliable.