The resolution of the boot splash is set by your system monitor resolution setup in XF86 so it is not likely that thats the issue. I would guess that the problem is eather that grub is set wrong or the package
bootsplash-theme-SuSE was not installed or your system startup was not compiled to use a splash screen.
To check grub open up YaST and under System click on bootloader. When it opens Click on "Edit Configuration File" then find the line for Linux
it should look something like:
kernel (hd0,5)/boot/vmlinuz root=/dev/hde6 vga=0x31a splash=silent desktop resume=/dev/hde5 showopts
Look to make sure
splash=silent
if it is setup than grub is set up right
Just pull open YaST Install Remove software to see if it's installed.
if neather of those fix the problem than the odds are that the splash image never got compiled into the system startup.
For info on that see
SuSE's site