Just follow what Cortona saids.
Depends on what level You beat it on.
http://guides.ign.com/guides/734817/page_2.html it is a guied to all of halo 3 (copy and paste)
If you are looking for a detailed guide, I would try YouTube for a level walkthrough.
Yes, you do. Otherwise, you cannot use the skull as an attachment or extra.
no.... im a holo freak.... in fact to get skulls in halo you find them when you play each level... so each level has a skull hidden in it... you just have to look for it...
No it does not. You have to beat every level.
wait for the next halo
To Get the E.O.D Helmet You Just Have To Beat Every Level on Legendary or To Get HayaBusa get all the skulls.
look on ign at a walkthrough it will give you a step by step guide with pictures
it comes with halo 3 ODST
Yes
Yes