GRAPELABS

You need an 320x480, 8bpp image, e.g. this one. Given it's name is splash.png, convert it with ImageMagick and ensure that the resulting file size is 460800 bytes:

Then you need to convert the image to the format that is used by Android. This conversion is done with a tool called rgb2565 which is found in the Android source distribution. You can download the source code here and compile it with gcc.

Ensure splash.raw565 has 307200 bytes!

If you haven't done so already, download the Hard SPL, put it onto the root of your Android SD-Card and power on your phone with the home key pressed. Select "install any update" and install the file splhard1_update_signed.zip.

Reboot with the camera key pressed. You should see skating Androids. Connect via USB to your workstation and press the back button. You should now read the text FASTBOOT in the middle of the display.

Download the Android fastboot tool from here. Now you are finally able to flash the splash image:

You should be greeted by your new splash screen.

Links:

forum.xda-developers.com/showthread.php

www.gotontheinter.net/logo.rle

code.google.com/p/android-roms/wiki/Install_Hard_SPL