Even if one changes the input to Dvorak on an admin account, the login window still defaults to querty.
I've yet to find a workaround... I just look at the keyboard when I log in. I'm guessing, though, that there is some pref file for the login window that could be hacked? I wouldn't know where to begin though.
Glad to see there is someone else here that uses Dvorak
On a related note, I think it was very clever for OS X to have an input mode that lets you do Dvorak when typing, but reverts to qwerty when you hold down the command button, so you don't have to re-learn keyboard shortcuts! (Unfortunately a few apps like Word and Photoshop don't recognize this )