Anyone built thier own media centre?

My flatmate and i both have mac books, We have an airport and all that jazz

Basically, we want to have a computer that we can both dump our movies, tv shows and music on wirelessly, and that can play these files via a LCD monitor.

we want to be able to play all video files (itunes only lets you upload mp4s???) so the apple TV is out. I also want to be able to upgrade it, bigger hard drives ect. I was thinking of getting a mac mini, but aparantly they are hard to upgrade?

Basicly, im thinking i should build a pc and run OSX on it... Has anyone done this? and if so... any hints?

If not... any ideas for me?

Thanks in advance.

There is a company that can install OS X on a PC, but I HIGHLY disagree with it. And, it's illegal, so I'm not sure if that's how you want to go. You can always convert files into MP3, too. Or download VLC.

But please, by all means, stay away from the illegal route. Not recommended.

Hope this helps