To install mplayer onto your Centos / RHEL distro you will need to :

1. Download and install the rpmforge repository.

rpm -ivh http://opensourcenuts.com/sites/default/files/rpmforge-release-0.3.6-1.el5_.rf_.i386.rpm

 2. Add the following text to a new file : /etc/yum.repos.d/fc6.repo.

cat > /etc/yum.repos.d/fc6.repo
[PASTE THE FOLLOWING]

[fc6-base]
name=Fedora Core 6
mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=core-6&arch=$basearch
enabled=1
gpgcheck=0

[CTRL-C]

 3. Install mplayer using yum.

yum install mplayer