It's not *that* hard. Buy yourself a 1 and a half inch chisel, then practice making spheres and cylinders and the like. Of course, getting the ice and obtaining a Dremmel or lightweight electric chainsaw are a bit harder.
As for the specifics, what you do is get a sheet of paper the size of your ice block, draw your picture on it, slap it onto the side of the ice, than trace it on. A dremmel works WONDERS for making this come out clean, so such is highly recommended.