The question is " boots/splash screen(s)" NOT desktop
Here we go:
1. Grub menu is managed by something called "gfxboot" in SuSE. Change theme in /usr/share/gfxboot/themes and read the file /usr/share/doc/packages/gfxboot/README Copy the resulting file to your /boot/message (make a backup first)
2. This is the bootsplash while booting: Download some bootsplash images from bootsplash.de http://bootsplash.org
Put the directory inside /etc/bootsplash/themes
For example "aqua"
Put your aqua theme in appropriate place: /etc/bootsplash/themes/aqua
edit the file: /etc/sysconfig/bootsplash
change the line Theme to "aqua".
execute (as root; backup the mkinitrd):
mkinitrd -b /boot -k <kernelname> -i <initrdname> -s 1024x768
The value for -s must be same as your image inside aqua". Remember if you have 16:9 screen it might be possible that different values like 1280x800 do NOT work. So, try with simple 1024x768 and experiment later.