I'm trying to install mythtv on Fedora Core 5. When I use the command yum install mythtv-suite i get this:

Repository core is listed more than once in the configuration
Repository updates is listed more than once in the configuration
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
Added 0 new packages, deleted 318 old in 2.04 seconds
Parsing package install arguments
No Match for argument: mythtv-suite
Nothing to do

I guess that I don't have the correct repo's in my yum.conf. If this is the problem, being the noob I am, I don't know where to get repo's from or how to enter them in yum.conf. Can someone point me in the right direction?

All the repos should be listed in files in /etc/yum.repos.d/. You probably have two .repo files that have core and updates in it, for some reason.
It's possible some might be listed directly in the yum.conf file, however that hasn't been the standard way of doing it since FC2.