AFAIK on Vista it's modifying resource dlls, well only one at the moment (the one with the background).
The logon screen uses resources from 3 dlls:
- imageres.dll : contains the background image, the waiting animation and the startup sound
- authui.dll : contains all the UI elements and the UI scripts
- branding.dll : contains the vista logo and vista edition name
You can have a look here
to get a little bit more related info.
BTW, emailing support to get technical info on the inner-workings of Stardock programs is not going to get you anywhere...