I had to reload my Mac OS last night, and after it was back up and running, with all of the latest 10.5 updates, i attempted to install and run RtDC.
I can only get as far as entering the registration info, once that happens i get the windowed black screen, and it will crash. no matter how many times i launch it.
I also attempted to run it on my imac for the first time, and i get the EXACT same issue.
I even re-downloaded the .dmg file with no effect.
Strange, I would say, try E-Mailing/Private Messaging Zack Black.