hard drive? Now that Microsoft allows USB flash drives to be used for storing data on an Xbox360, what are the disadvantages (if there are any) of buying an Xbox360 arcade and using 2 USBs that provide 20 gigabytes for a hard drive, as compared to buying an Xbox that already has a hard drive of 20 gigabytes?Just trying to find the cheapest way to get another fully functioning Xbox, intended for online play and would also expect to want to download game add-ons such as map packs from marketplace. Please include any sources used.