If you are installing rpm files by manually installing them, that's not the best way to go about it. The best way to go about it is to use yum. Yum is a package manager that automatically downloads and installs dependencies for you.
Step 1) Set up yum. This basically involves modifying your /etc/yum.config to include yum "repositories" that contain software. A pretty good sample yum config file can be found here: http://www.fedoraforum.org/forum/arc...hp/t-2067.html (the second post down contains a decent starter list)
Step 2) Install! I believe freshrpms.net has mplayer and all its dependencies, so make sure that the freshrpms repository is listed in your /etc/yum.config file. Type "yum install mplayer" as root user and you're off! The first time you run yum, it's gonna take a LONG time. LONG time means walk away for a while. It will take a look at the repositories you gave it and construct a list of what's on each one. This will take 20 min to a half hour or so. After that it's a little better.
Hope it works!