G1 Splash Image
The splash image for the G1 and ADP1 is stored in the 'splash1' or 'misc' flash partition, and displayed by the bootloader on startup.
It it stored in a format that can be directly written to the frame buffer for the screen by the bootloader. The file must be exactly 320 x 480 pixels, in raw '565' format. The file should be exactly 307200 bytes.
To write your own splash image to the phone, you need to create the image file from an existing picture, then use fastboot to write the image to the 'splash1' partition.
For detailed instructions, see: http://www.gotontheinter.net/logo.rle