Modify Windows Login screen

Is it possble to Modify the Window's Login screen and add our own buttons/links? For example is it possible to do something like this?

alt text http://www.allaboutmoss.com/wp-content/uploads/2010/04/windowsxp_login.jpg

The 开发者_开发知识库above screen has a link and when clicked it should start a win forms application?

For Windows XP, you can build a GINA DLL, and for Vista+ you need to use the new credential providers system. In both cases, you basically have to build the UI from scratch and so it's not really possible to just take the existing UI and add a few controls here and there.

Of course, you could build your own GINA DLL that displays UI that's the same as the standard Windows XP one, with your own additions, but it's not exactly a simple task.