Could someone help me get the Tilt Skull in halo 3?

[David]

I need someone to give me their gamertag and do co-op over xbox live to get the skull. I have tried but cannot find it. I know its on "Cortana" but I cannot seem to find the skull. My gamertag is "X221".
oh ya also whoever helps me gets 10 points

 

[Nevo]

omg its ezy i got all the skulls look on youtube