Unfortunately I don't know debian, but here is a link to a bunch of Howto's for Debian http://www.howtoforge.com/howtos/linux/debian and I know that in Ubuntu it is very easy to change your logon screen and such, just like changing the wallpaper in windows. Maybe if you try to search for a program that allows you to so type in your terminal:

sudo apt-cache search logon

or something similair, the list of packages containing the word logon will be shown. I hope it helps you.