Hi there,
Like the 5000 & 6000 series Zauri, first of all you need to rotate the image 90-degree clockwise. Then ensure the image is a 480x640 24-bit BMP.
Then, as root, save the file as Startup_screen.bmp and copy to /home/QtPalmtop/pics overwriting the existing file there (You might want to copy the existing file for backup first!).
Finally, create a new symlink to it in /home/QtPalmtop/pics144
That's it! I've attached the screen I use on my Zaurus SL-C3000...
Russell