Adding a skin to a windowed application

i'm working on a project that entails making a program with the look and functionality of a drum machine. whilst i think i can manage functionality, i've been wondering how on earth i can make it "look" like a drum machine? is it easy to substitute a window look with a self-made one? i'm not planning on doing this immediately but a general idea would help put my mind at ease :)

thanks

They're called skins. Search the forum - people ask about them all the time.