Not actually a customization - but rather information on how to alter the startup splash screen ..
The splash screen is located in the horizons\resources\interface\themes\default\textur es\startup dir.
The file that shows is called HzSplash.bmp
It would appear that Vi is making it so that you can choose the splash screen of your choice as there are 16 different options in there .. but in the meantime if you change any of the splash_#.bmp files to HzSplash.bmp it should load that one instead of the dryad one that some people do not like so much.