I'm going to help you out a bit. I've attached an installer script, the only thing you have to edit is the theme name. This was written by Towheed Mohammad here about a year ago. I know he has an updated version, but this one works just fine. I assume that you're going for a resolution independent theme, so the tweak I did to Towheed's installer should make it easier for your users to modify the resolution.
I'm also reading through your todo.
-Avoid scrollbars, they're more trouble than they're worth, and don't really add much to the theme. So set scrollbars to false.
-Make your terminal background larger (which is why it's not working). Grub doesn't like images smaller than 2x2.
-For the navigation label, I recommend creating it in Gimp and adding it like an image. You get the benefit of antialiasing.
-Also make your font larger.
-Your progress bar looks messed up because on the center piece you have a one pixel transparent border on the top and bottom.
-My personal preference is for text to not be on the progress bar, to do this you just set text = ""
-I'm not sure what your issue is with the 1024x768 resoluton is or with your selection images (doesn't stretch all the way?).
-If you want to add a drop shadow to the terminal and the menu, just reconstruct the full images in Gimp, combine them all, do a drop shad (Filters -> Light and Shadow -> Drop shadow),then cut them back up (you'll have to change some parameters in your theme.txt).
-When testing it the selection center part is completely missing. I don't know why that is.