I have a laptop used for playing music (and occasionally also videos) which is currently running Windows XP with XBMC. Reinstalling this beast to Linux is on my todo list for ages and now I've finally found time to try that.
Starting Debian installer worked like charm and in few minutes I got Debian system running. I've chosen to run sid, well for reason I run it usually on place where I want latest software. Installing XBMC from Debian multimedia worked also fine and you can easily find some howtos for directly starting XBMC.
And that's where I ran into trouble - XBMC is damn slow. Notebook has oldish nVidia GeForce FX Go5200 card, which seems to be poorly supported by nouveau (and "Do not file bug reports about this driver." suggest that this is what authors do expect). Okay, I can survive having some binary crap so let's try nVidia proprietary drivers. I've quickly realized that the legacy drivers won't work with recent xserver and probably also not with the kernel.
Maybe I should try installing something older, what would run binary drivers, but for now I gave up and system is back on Windows (with all problems I have there...).
It seems XBMC uses OpenGL heavily. So on any graphics card where DRI is not working properly you are going to have issues. I remember it being very sluggish on an old installation with Radeon 7000 card. But I would also suggest trying the XBMC 11.0 beta (in case not tried already) before replacing the card.