1. Install HardSPL.
2. Create a BMP file in paint, size must be 240x320, save it as BMP 24bit.
3. Download SplashTool
4. Load your BMP on nb_image_converter (included in SplashTool's zip) and save it as splash.nb
5. Open SplashTool.exe and convert splash.nb to new format.
6. Pack the resulting splash.nb into a NBH file using htc rom tool.
7. Flash your cusotm NBH using CustomRUU.
Enjoy your new splash screen!