Whilst a Mini can unofficially run WMC (search the forums for how) I'd suggest that a mini (even the lowest model) with an external hard drive and an eyetv works just as well, if not better than WMC.
My set up:
Mac Mini - 1.66Ghz - Combo Drive - 1GB Ram - 80Gb Drive (feel free to get the higher model mind, has a superdrive as standard if you plan on burning off any recordings)
iOmega Minimax 250GB Hard Disk Drive - so I have room for all my media - set up an alias in the movies folder so front row can see the video, and point my recordings here too.
An EyeTV - mine is a basic one from some time back, however get whatever the current model is that suits you now.