####### /etc/apt/sources.list 
# cat /etc/apt/sources.list
#deb file:///cdrom/ sarge main

deb http://ftp.debian.org/debian/ stable main
deb-src http://ftp.debian.org/debian/ stable main

deb http://security.debian.org/ stable/updates main
deb http://www.backports.org/debian sarge-backports main

######## apt-get update result
# apt-get update
Hit http://security.debian.org stable/updates/main Packages
Hit http://security.debian.org stable/updates/main Release
Err http://www.backports.org sarge-backports/main Packages
  500 ( Not implemented  )
Hit http://www.backports.org sarge-backports/main Release
Hit http://ftp.debian.org stable/main Packages
Hit http://ftp.debian.org stable/main Release
Hit http://ftp.debian.org stable/main Sources
Hit http://ftp.debian.org stable/main Release
Failed to fetch http://www.backports.org/debian/dists/sarge-backports/main/binary-i386/Packages.gz  500 ( Not implemented  )
Reading Package Lists... Done
W: Couldn't stat source package list http://www.backports.org sarge-backports/main Packages (/var/lib/apt/lists/www.backports.org_debian_dists_sarge-backports_main_binary-i386_Packages) - stat (2 No such file or directory)
W: You may want to run apt-get update to correct these problems
E: Some index files failed to download, they have been ignored, or old ones used instead.