Dustin is correct - copyright covers things that can be copied (generally), like books, pictures, etc.
Copyright law can get fairly messy and then you can throw in international copyright law to make it even messier!

Since you are talking about US coins, I will suppose that you are a US citizen. In that case, to study copyrights, I suggest
http://www.copyright.gov/ which will give you what you're looking for.
Regarding the coins, though, you're really talking about patenting and that costs a
HUGE sum of money. In fact, generally, the cost of a patent far outweighs the value of an item that you are looking to manufacture unless it's going to be mass produced or has a large market (and magic isn't really a large market).
Further, how do you know that AUS coins are not already covered under a patent? Just because they aren't being made doesn't mean that they aren't patented. Even if they aren't patented, does that give your friend the right to rip off someone else's idea (particularly to make a profit)?
And, before I forget, what the hell are AUS coins?
Anyway, just some stuff to think on.
Mike.