I don't think there are requirements for "this is how a cd cover looks like" ...it's a design use your imagination. All you need to do is pick a size to work with. This is usually given to you by the person hiring you to do the book cover, CD case whatever. Once you know what size you're working with... GO NUTS!
Ah.. so you're not actually designing any printed materials, you just want to create web graphics that look like those objects?
Hmm... I don't know of any step-by step tutorials for creating specific objects in Photoshop. Most PS tutorials tend to cover things like how to apply certain effects to or correct flaws in existing images.
Have you considered purchasing a large clip-art collection? Then you could find generic images of the objects you need, and edit the images to suit your specific designs.