There are 3 options if you want to have a skin
a. buy the game
b. get mineshafter (only other players with mineshafter will see your skin)
c. Replace the default skin in your minecraft jar (only you will see your custom skin&you will see everyone wearing the default skin wearing yours)
If you want a hacked client just install one. You don't need a premium account to do that. Just replace the original minecraft jar with the client's jar file