ill give ya example of how i use stock and renders...
heres the finished product of the last wall i made


i used these two other wallpapers to make it... i erased everything from this one but the girl (takes FOREVER but its easy)


and i overlayed it onto the top right section of this picture of new york city


i did all the effects and text by hand.. mehhakker gave me tip about the effects behind her.. the flame is a smoke brush with a simple color gradient applied to it...
if you really want to check out how i did it and you use photoshop here the psd... take a look.. that's how i learned what i know lol
psd - http://www.megaupload.com/?d=909I2IWO

im no expert but i know a few tricks lol