You don't need to do su, if you've installed sudo just simply do.
This is assuming you're on a 32-bit system.
Sudo apt-get install libsdl1.2debian libsdl-mixer1.2 libsmpeg0
This would be the good to use, I'd also make sure you install both the 64 and the 32 bit vers. so that you can guarantee any 32-bit libs aren't needed for some strange reason...
Sudo apt-get install libsdl1.2debian:i386 libsdl-mixer1.2:i386 libsmpeg0:i386
You could also just go whole hog and either install ia32libs or lib32z1 The first is for the 12.04 LTS, but the other is for 13 and above in Ubuntu.
I'm not sure about Debian, but I'm assuming it's a similar system.