You could always look into XBMC. You can actually make an extermal player, MPC-HC for example, the default player. I've done this in the past, its a great combination. You get the UI of XBMC and all the benefits a player like MPC-HC has as a player (decoders, post processing, renderers ect). Here's a screencap I took:
(PS that white bar at the bottom was only there when the movie started because my mouse was at the bottom of the screen when the movie started, it starts up and plays seamlessly as if you weren't using an external player)
It's pretty neat and its fairly simple to set it all up. I've got my desktop and a raid tower with ~20TB of content most movies and some TV Shows, That combination wows anyone who sees it. All my friends are pretty impressed.