Your best bet is Kasdians Overhaul Guide. Search the forums for 'kasdian' and i'm sure it will crop up.

You may be dissapointed tho cause you are fairly limited in what you can do to existing ships. As all the textures have already been mapped in the .cmp file you only able to exit the texture itself, not where is is placed on the ship. Most ships only use a few patches of texture which are mapped to multiple locations. This allows you to make the ship lighter/darker, a different colour, checkered or whatever but you wont be able to put a huge skull and crossbones on the underside or anything.

Unless someone has made a .cmp exporter and i've missed it (quite possible ) your best bet for customized skins is putting them on a custom ship.

thank you