like i see it

(i have download it and look at the code and pictures, but i haven't try it cause my max resolution is 1280x1024

) i could run only in your resolution cause of the alignment of the panel account and wallpaper set at stretch (it's good with many wall but with an orb that can't run good for other resolutions).
That's really cool i don't know it was possible in a dual monitor.
So maybe a Splash could allow you to make a logon for your and also for under and higher resolution.
My english not allow me i think to explain mine idea well but i try:
If you could fix the wallpaper not in stretch and the Bitmap_128 (means the panel account) on the left border at maybe 500 px of this border. that could run for more resolutions.
I'm not an expert in logonxp.
So here i think we need a expert like Boss019 to help us.
I'll try to see what i can make with the code.
Anyway your logon looks pretty good and i love the wall. And i think you aren't the only with a dual monitor so it's a very good idea