wordpress theme generator

ive just found this,looks pretty neat to me but im easy pleased http://www.yvoschaap.com/wpthemegen/

Here it is, I want to make wordpress themes. And to be completely honest I dont know the first thing in creating them. Im not good with php or css. But i want to be able to bang out at least a few with no problem. Now if i go to wordpress themes and download an existing site can I...