Why thank you, cyberderf!
I am not entirely about the 'screened lines' you refer to, as the image in the screenshot appears smooth to me. However, I do believe I know what you're talking about, as the finished versions at [link] and [link] do have an alternating pixel lines effect. I did this simply by using The Gimp's "Stripes Fine" pattern fill on a layer behind the subject image.
Hope this answers your question. If not, let me know!
I'm pretty sure the Gimp and Blender are the two most mature graphics apps in the open source world. I highly reccomend them, I've used them along with inkscape practically exclusively for everything in my gallery! I'm planning a tutorial on using them together with inkscape to make wallpapers for my next major deviation, so stay tuned!