I played a bit with the matrix theme at kde-look.org. And indeed, this was quite funny to see a (static, though) matrix image at early boot, then at system startup, and also as a KDE (which the desktop I am using) startup splash. I just miss the kdm background and desktop backgrounds and I'll have a consistent matrix in front of me!
If you want to see that at normal system boot, change your kernel command-line to have theme:matrix.
I know this is not really uniform; now I realise that; and I will try to fix it in the next releases of splashutils.
2 - matrix-grub-theme
You will need to replace grub with grub-gfxboot. Packages for i386 and amd64 are at: this page describing grub-gfxboot installation! Please take care, and make sure you reinstall grub as explained at this page! The deb location is:
# Grub gfx boot
deb http://www.nanolx.org/apt excelsior main
Then you will just have to add a line like (this is what I did):