ok my bro is at the shop and is going to buy me either the xbox 360 20gb or 120gb. does he need to shelve out the extra money for the extra space? i will only be playing games and will never ever store movies or music on it. also can't i just buy and external HD for it later? i heard the PS3 actually needs games to be installed to it. is this true for the xbox 360? if so will that limit the number of games i can play at a time?