Ok I can guide you in this one Warlock.
Skulls:
The Skulls were first introduced in Halo 2's campaign missions as easter eggs for people to find and in doing so they activated mysterious effects, mostly on your foes rather than being supportive towards you. They return in Halo 3's campaign levels and are now able to be activated on any mission once obtained. There are a total of 9 Gold Skulls and plus 3 secret silver skulls to be found. Once all have been found they give you Hayabusa Armour Permutation. Go here to find out on where to locate the skulls:
Halo 3 Skulls
Warlock you should also ask your friends online as they would likely to have found them as well by themselves or with the help of others. Or just look it up, there are tonnes of guides on finding the skulls. I think this website should help you otherwise. Don't go to it if you want to seek out the skulls alone, be warned they are tricky to find.
Oh and my multiplayer armour is an Elite with Ascetic Helmet, Commando Shoulders (yes they finally removed the glitch for Commando shoulders a month ago!) and Combat body. My primary colour is Sage (seeing as it is a pure green colour, the normal green colour looks bad in Halo 3) and secondary is Gold with Crossed Swords as my emblem (I also go with the Snake Emblem sometimes).