Great walk-through
wile going through the steps i came across two dimensions that are slightly off
this really only matters if you want an exact fit, and i was creating an exact fit wallpaper
the lower part should be 480x184, so the whole image has to be 480x696
the landscape wallpaper should be 800x376, so the right part will be 512x376 and left 288x376
this is all discussed in more detail here
thank you for this walk-through
Is the line gone when you do the dimensions this way?