you are using el5.i think you dont have liscence key of that..
so you need to enable repos by manually..
normally if you have license..through RHN you can download packages...
if you have good internet connection..go to players website..and download source file..then install..
if you want to work with yum-you need to do some settings to your yum.repos.d...
i hope it will help to you to get out that problem..
but with out RHN support its very difficult to use el5(i have used recently)
but ways are there..you need to work around that problem..