Type the following comand from telnet
mount /boot -o remount,rw
delete all sym links from /boot
delete all *.mvi files from /usr/share including the sym links
then type from telnet
ln -s /usr/share/backdrop.mvi /boot/backdrop.mvi
ln-s /usr/share/bootlogo.mvi /boot/bootlogo.mvi
ln -s /usr/share/bootlogo_wait.mvi /boot/bootlogo_wait.mvi
copy the attached files to /usr/share

or

umount /boot (sometimes not needed)
mount -t jffs2 /dev/mtdblock2 /boot

and you will find files that should be the one you want to change, keep the exact same size/format/definition/color/dpi

bootlogo-dm8000.jpg
bootlogo-dm8000.elf.gz

Format : 72x72 DPI, 1280x780x24BPP (16.7 Millions colors 24 bits per pixel)

Enjoy

Then to change the boot logos just find ones you like on the net and replace the files in /usr/share if you dont like the ones I posted

You cal also use this Utility.

Dream BootLogo Generator - VU+ and Dreambox 800/8000

Here is a Software to automate things a little:

1: select a file. JPG 1280 x 720 and then convert it into. MVI
2: send to your Dream FTP

WARNING: This version only works with VU+ /Dreambox 800/8000
This is currently a Beta and other versions will follow may be to manage other models.

There might also be newer versions of this app.