if you are trying to get the amd64 sarge release from debian.org that would explain your problem. debian only officially provides amd64 security support for sarge. see http://amd64.debian.net/ for more information (specifically http://amd64.debian.net/README.mirrors.html for installation mirrors and http://amd64.debian.net/docs/ for documentation).

as part of my vserver setup i use apt-proxy, so that the updating/upgrading of one vserver caches the packages locally for the other vservers to use when i update/upgrade them seconds later. and creating new vservers in really quick as i've pre-cached both sarge amd64 installation dvds (see apt-proxy documentation on "importing").