lol no, sorry misunderstanding on my part :P
Are you using eyefinity or something of the sort?
edit: if you are heres something that might help: http://www.figure.fm/post/en/3494/Customising+Windows+7+logon+screen.html
follow the steps, but choose a picture:
- that is the full resolution of your setup
- that is less than 256kb (few colors or graphics): optimize images with this http://www.imageoptimizer.net/Pages/Home.aspx
and hopefully it will work