i dont think MS has ever officially said anything about the OS size for 360, but from what ive read, various devs have made comments, which range from 24-32MB, bare in mind the 360 OS has had like 10 years development (its based on windows 2000 -> xbox os -> xbox 360 os) so its incredibly efficient and low memory footprint, not to mention MS has been in IM client game forever too, now if only they made the GUI more streamlined like i have my windows ;/ i hate chunky GUIs (im looking at you xp and osx)