Basically, you'll want to use "yum", in the terminal.
I guess you know that to become root, you have to use the "su" command.
Get a decent set of sources in /etc/yum.conf (you'll need to root to edit this, and the sources are the download sites with programs on them - examples being atrpms, freshrpms and so on, use google to find the details you need to add to the file)
then as root: yum install amsn
to find more software: yum search (name or word in the name of software)