why white? don't know, i just like white
there is an example with a black background, but it loses the point...
Should work in any existing resolution.
Feel free to modify it by changing the background colour or adding pixmaps (images) or text somewhere. The .xml file is easy to edit.
EDIT: I realized that there is actually a greeter like this. Almost identical. That theme is SimpleGreeter by DerQ:http://www.gnome-look.org/content/show.php/SimpleGreeter?content=62313
I must say that my theme was written completely by me, as a simplification of my V-Login greeter ("I" letter), so any similarity is just coincidence. (just take a look at the xmls)