well, the epu mobos are tricky!
you may crossflash your mobo, to a plain p5k-se
but, first, try that
be sure your first sata connector is on your first hd, and your second sata connector is on your first DVD
try to boot it now
if that fails, crossflash your mobo, but be sure what your are doing. Else, it should work.
I'm trying to install SL on my Asus p5k SE/EPU with the rebel EFi as you wrote earlier but i can't get past the 'no smoking' sign when the retail SL is starting after i inserted it.
I've read the Rebel EFI needs AHCI but my bios doesn't support it. I read an older bios does but is this why i can't get past the 'no smoking' sign?