^ As I undersatnd it you'll be able to do both.
Here's why.. (quoted from the front page)
XBMC team will be working to improve the experience on
the rPi, and that various distros like raspbmc will give you choices
for how to deploy it, but we’re not the same organizations.
This means you'll be able to take XBMC and install it on your "PC Style OS card", or use a card that has the same XBMC thats been bundled into the (mostly) pre-configured distribution by the RaspBMC people.
(I say mostly as it obviously won't include specifics like where your media library is, and information about your network)
Pi Status > Farnell, Arrived 24/5- RS, Arrived 1/6