apt-get is the program that does all the work,
---> synaptic is only a front-end, or GUI part of apt-get.
Edit the "sources.list" file found in /etc/apt/ directory.
Add these lines (replacing the Redhat 9.0 section):
# Red Hat Linux 9
rpm
http://ayo.freshrpms.net redhat/9/i386 os updates freshrpms
### Dag Apt Repository for Red Hat 9
rpm
http://apt.sw.be redhat/9/en/i386 dag
### linuxwiki.org - a german repo
rpm
http://ftp-stud.fht-esslingen.de/apt redhat/9/i386 os updates
### vlug - another repo
rpm
http://vlugnet.org/apt redhat/9/en/i386 inoupdates vlugrpms