Halo 3 Catch skull help?

[nuttrong]

I asked this earlier here http://au.answers.yahoo.com/question/index?qid=20090202233903AAcoVCu but the people who responded were absolutely no help. I do exactly as they say but the skull won't come.
I even went on theater mode to see if it were to appear but disappear again but it never came.

I need real help thank you, not just copied and pasted stuff that I will find useless.

 

[theville812in]

kill the enemys so they dont kill u BUT DO NOT KILL THE SECOND WRAITH (furthest from where u enter the battle ground) Drive the warthog to the tower things in the middle stand on top of it and throw a granade on the wart hog(plasma would be best) and just with the explsion...its up there...
IF U DONT GET THIS THAN WATCH THE VID...

http://www.youtube.com/watch?v=sdmawJhMAWY