in Planet Software hardware-hacking Thinkpad ~ read.

BIOS Bootsplash for Thinkpad (T41)

On I found 2 articles how to get rid of the IBM BIOS Bootsplash and your own working. One for Windows and one for Linux.

At first, you need 1ruj35us.exe or newer. With

# cabextract -F "*.IMG" 1ruj35us.exe

you will get a 1RUJ35US.IMG, which is a floppy image.

Next you need to create a 16 color 640x480 BMP and save it as /tmp/logo.bmp. Now we need to mount the floppy, let the "logo.bmp" take place there and generate a "logo.mod":

# mkdir /tmp/floppy
# mount -o loop,umask=000 /tmp/1RUJ35US.IMG /tmp/floppy
# cp /tmp/logo.bmp /tmp/floppy/ && cd /tmp/floppy/
# wine prepare.exe logo.scr
# cd && umount /tmp/floppy/

If you don't have wine, but a running windows in place, use Virtual Floppy Drive like described in the Windows instruction to get the picture on the disk image.
Now you only need to burn a CD(-RW) with 1RUJ35US.IMG as boot image. This can be easily done with k3b or on console:

# mkisofs -b 1RUJ35US.IMG 1RUJ35US.IMG| cdrecord \
 dev=<device> -

You only need to boot your Thinkpad from CD(-RW) by pressing F12 on boot and flashing new firmware with customer image. You are done! My bootsplash image can be found here, an 'unbranded' one here.