Some games require a 4GB harddrive. It's a dated reference, but I one of the NHL 2K(something) games never saved and we were stuck with the exhibition games without the season play. Point is, some games just kind of require it, I guess. I can't find anything beyond the system requirements, but no reason for them. It might be a precaution or something, on the off chance it needs your drive to save maps and such, but I really don't know for sure. I'll let you know if I find anything. You might have to spring for a new harddrive (your system's slot is most likely empty if you have anything made after the original 360). Luckily, they are not too expensive. Best Buy has the 250 GB (which is more than enough) for around $50 and 500 GB for about $100. It sucks, but that would be your only option. And as for GRaVE's assertion that only Xbox is having issues... aside from not being helpful or understanding the point of the help forums, the PS3 also requires around 40 GB free, so the shorthand ones would also fall a bit short.