I am not sure if that would work with the rpm.
You should try compiling from source it was surprisenly easy, infact, mplayer was my first install from source. Goto the mplayer home page and download the Mplayer0.92.tar file
then unpack it with the command
$tar -xvf exact_name_of_mplayer_package
$cd to the new untarred file
look for a file called README, it will tell you exactly what to do
also you will need to install your developmentel packages(before you can compile mplayer) off of your redhat cds, goto add/remove programs and install them.