I'm making this thread to help find all the skulls in Halo 3.
Halo 3 has a scoring card which you have to enable in the campaign menu.You can do it for co-op and single player it will keep track of how you play the game and base a score on it.
if you are in co-op its up to the party leader to enable scoring and choose the skulls he wants enabled or disabled and the scoring mode.
to read more about it:
Bungie.net : Inside Bungie : News
they won't tell were the skulls are so I figure if you find a skull on a level you could post the level and place you found it.
the highest score you can get in Halo 3 is on legendary with all the skulls enabled,which would be very hard as one of the skulls
turns your radar off another gives the enemy twice the hit points
just to name a few.
good luck finding the skulls.