Link : Xbox portable
image portablesystems.net
These guys have actually turned a xbox into a portable game machine 
“This project took about 60 hours to complete from start to finish. My portable Xbox will run off the built in batteries or you can use a ac adapter. Im not sure about battery time because I just finished it but I will be testing how long it will last when I get the time to play it for that long. The hard drive is a 60 gig seagate laptop drive. The reason I went with a laptop drive is it’s small and it runs off 5v. The LCD screen is a PSone screen and I did a LED mod on it.”