• I have Debian 4 server (i know it is very old)

  cat /etc/issue
  Debian GNU/Linux 4.0 \n \l
  

• I have the following in /etc/apt/sources.list

  deb http://debian.uchicago.edu/debian/ stable 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
  

• apt-get upgrade

  Reading package lists... Done
  Building dependency tree... Done
  You might want to run 'apt-get -f install' to correct these.
  The following packages have unmet dependencies.
    libt1-5: Depends: libc6 (>= 2.7) but 2.3.6.ds1-13etch10+b1 is installed
    locales: Depends: glibc-2.11-1 but it is not installable
  E: Unmet dependencies. Try using -f.
  

• Now it shows that i have Debian 6!!

  cat /etc/issue
  Debian GNU/Linux 6.0 \n \l

EDIT
I have tried

apt-get update
Get: 1 http://debian.uchicago.edu stable Release.gpg [1672B] 
Hit http://debian.uchicago.edu stable Release
Ign http://debian.uchicago.edu stable/main Packages/DiffIndex 
Hit http://debian.uchicago.edu stable/main Packages 
Get: 2 http://security.debian.org stable/updates Release.gpg [836B] 
Hit http://security.debian.org stable/updates Release 
Get: 3 http://ftp.debian.org stable Release.gpg [1672B]
Ign http://security.debian.org stable/updates/main Packages/DiffIndex
Hit http://security.debian.org stable/updates/main Packages
Hit http://ftp.debian.org stable Release
Ign http://ftp.debian.org stable/main Packages/DiffIndex
Ign http://ftp.debian.org stable/main Sources/DiffIndex
Hit http://ftp.debian.org stable/main Packages
Hit http://ftp.debian.org stable/main Sources
Fetched 3B in 0s (3B/s)
Reading package lists... Done

apt-get dist-upgrade
Reading package lists... Done 
Building dependency tree... Done 
You might want to run 'apt-get -f install' to correct these.
The following packages have unmet dependencies.
  libt1-5: Depends: libc6 (>= 2.7) but 2.3.6.ds1-13etch10+b1 is installed
  locales: Depends: glibc-2.11-1
E: Unmet dependencies. Try using -f.

apt-get -f install
Reading package lists... Done
Building dependency tree... Done
Correcting dependencies...Done
The following extra packages will be installed:
  gcc-4.4-base libbsd-dev libbsd0 libc-bin libc-dev-bin libc6
Suggested packages:
  glibc-doc
Recommended packages:
  libc6-i686
The following packages will be REMOVED
  libc6-dev libedit-dev libexpat1-dev libgcrypt11-dev libjpeg62-dev libmcal0-dev libmhash-dev libncurses5-dev libpam0g-dev libsablot0-dev libtool libttf-dev
The following NEW packages will be installed
  gcc-4.4-base libbsd-dev libbsd0 libc-bin libc-dev-bin
The following packages will be upgraded:
  libc6
1 upgraded, 5 newly installed, 12 to remove and 349 not upgraded.
7 not fully installed or removed.
Need to get 0B/5050kB of archives.
After unpacking 23.1MB disk space will be freed.
Do you want to continue [Y/n]? y
Preconfiguring packages ...
dpkg: regarding .../libc-bin_2.11.3-2_i386.deb containing libc-bin:
 package uses Breaks; not supported in this dpkg
dpkg: error processing /var/cache/apt/archives/libc-bin_2.11.3-2_i386.deb (--unpack):
 unsupported dependency problem - not installing libc-bin
Errors were encountered while processing:
 /var/cache/apt/archives/libc-bin_2.11.3-2_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

Now: it seems there is a conflict!! how can i fix it? and is it true that the server has became debian 6!!??
Thanks for your help