What MT is talking about (I'm assuming) is taking an existing product shot and replacing their logo text with something made up. You actually see this a lot if you look at the t-shirts in sk8r shops or the like.
This mostly, in my experience, involves finding a font that will work with the existing one, removing the existing logo with cloning or package reconstruction, and then simply adding your text to the image.
Check out this site to see a sampling of "product" related fonts to get an idea of what kind of things are available.
http://www.dafont.com
Mostly this just involves patience and careful painting skills to remove the old text.
$0.02