Ive had mine sitting on a seperate table with lots of open airspace. THe power brick is on the table too. Not sitting on the carpet I was first shipment of the original xbox machines. Never had a problem with it. still going strong.
You need lots of open airspace, and not have anything impede its airflow. Its no different than a pc, its suppsoed to have x ammount of airspace arround it. typically if you provide that you should be ok.
