We have had some issues with the apt that is currently in the Extras repository properly resolving some dependencies in CentOS.
http://bugs.centos.org/view.php?id=1416
http://bugs.centos.org/view.php?id=1502
There are new apt and synaptic packages currently in the CentOS-Testing repository that correct these problems. The new version of apt also can use repomd repositories ... and the next version of CentOS-Release will contain a sources.list file that uses repomd and not rpm type repos for apt.
The new RPMS are: apt-0.5.15lorg3.2-1.c4.i386.rpm apt-devel-0.5.15lorg3.2-1.c4.i386.rpm synaptic-0.57.2-3.c4.i386.rpm
Available here: http://dev.centos.org/centos/4/testing/i386/RPMS/
Thanks, Johnny Hughes
#--------------------- # Example repomd repos for apt # URL: http://www.centos.org
### CentOS-4 APT repositories repomd http://mirror.centos.org centos/4/os/i386 repomd http://mirror.centos.org centos/4/addons/i386 repomd http://mirror.centos.org centos/4/extras/i386 repomd http://mirror.centos.org centos/4/updates/i386 repomd http://mirror.centos.org centos/4/fasttrack/i386 #repomd http://mirror.centos.org centos/4/centosplus/i386 #repomd http://mirror.centos.org centos/4/contrib/i386 #repomd http://mirror.centos.org centos/4/csgfs/i386