LinuxMCE is a better choice for a full OS. MythTV is more of a replacement/improvement for a TiVo style machine; it's best for set-top boxes on which it will be used almost exclusively. It's quite nicely featured now, with even a web browser optimized for couch-surfing.
If you do want MythTV based on Fedora the easiest way to set it up is using MythDora, a MythTV distro based on Fedora Core 6.
/goes back to designing and building my new Myth setup...