I don't have much experience with this stuff but the concept is pretty simple
First find out how much required power is need for the LEDs
After knowing your required power find a point on the motherboard using this post
http://team-xecuter.com/forums/threads/84670-Power-Sources-Switched-and-Standby
Wire it up to that power making sure you grounded your negative terminal to an audio connecter and your positive is wired to the pad where power is provided
Test to see when you pwr on the Xbox ur leds turns on
Make sure to connect led strips in parallel if u cut any to fit in the xbox