TCK

Not sure if this is what's causing your issue, but in Kubuntu I had to go to the System Settings and change the user image source setting on the login screen before anything would come up.

System Settings > Login Screen > Users tab.

By default I believe User Image Source is set to System, I've changed it to User, System. This way if you have an image associated with the login this will show, if no image is associated with the login a default image will load. You can also set the default image in this section. - Jul 20 2012

Not sure if this is specifically the issue you're facing but I have had difficulty installing directly from the "Get New Themes" section. My solution is to download the .tar.gz file from OpenDesktop.org directly and install it using the "Install new theme" option.

If this still doesn't work, you can copy the folder in the downloaded file to /usr/share/kde4/apps/kdm/themes/ - this will then appear in SystemSettings as an option to select.

(Note that this is based on Kubuntu 12.04 32-bit - doubt it'll be any different for 64-bit though.) - May 07 2012

Wasn't aware of that, good point! Problem is I'm not sure whether the KDM theme I based this on is similar enough to require CC licencing or not as the code is mostly based on the Caledonia theme. Does CC apply to images only or the whole work? - May 07 2012