si, entonces es normal
Mira estos datos sacados de las FAQ del XBMC:
XBMC capability on a standard Xbox (Intel 733Mhz PIII CPU):
720x480p video output to 720x480p = OK! (eg not upscaled).
720x480p video output to 1024x720p = OK! (eg upscaled to 720p).
720x480p video output to 1920x1080p = OK! (eg upscaled to 1080i).
1024x720p video output to 1024x720p = FAIL! (eg native 720p).
1920x1080i video output to 1920x1080i = FAIL! (eg native 1080i).
Note! All above that sais FAIL don't actualy fail to play, it's just that the Xbox CPU is to slow to decode and render the high resolution so they will play so slow (dropped frames) making it unwatchable.
Para que no pase eso, hay un mod por ahi, para cambiar el micro por una de 1440 Mhz, pero no debe de ser nada facil, porque creo que lel micro viene soldado a la placa, una pena