If you setup the livna repo and import the gpg key with this command:
rpm --import http://rpm.livna.org/RPM-LIVNA-GPG-KEY
Then you should be able to install mplayer with the command:
yum install mplayer.i386
The package seems to be from livna-unstable so you may need both of these repos
Code:
[livna-stable]
name=Fedora Extras
baseurl=http://rpm.livna.org/fedora/3/i386/RPMS.stable
enabled=1
gpgcheck=1
[livna-unstable]
name=Fedora Extras
baseurl=http://rpm.livna.org/fedora/3/i386/RPMS.unstable
enabled=1
gpgcheck=1