OSX can run on standard intel. I have it running on a P4 3.2 here but it's far nicer/easier to get running on a C2d on a latter motherboard. The Gigabyte P35-DS3 series being the best of the bunch at the moment.
Note though that making it run on standard intel is a hack and is technically illegal, even if you buy a retail copy of OSX.
If you want to check it out though it's not a bad way of doing it before shelling out for a Mac mini or suitable real mac.
XBMC info and screenshots etc can be found
here.
It's fully skinnable. One of the best going around at the moment is
this one.
XBMC looks feels and acts the same on the Xbox 1, Linux and OSX so the screenshots are valid for any platform.
Cheers,
Arkay.