Program the SB128 ?? I'm confused here, what is it you want, to create a program with which you will be able to change hardware settings on the card ?
Or just some music program, that will play a given file, and use the SB128 as output?
For the last one you just need to open /dev/dsp in a nonblocking way, then pipe to it what ever sound you want to output.
For the first one, you'll need to find the specifications for the hardware, a thing I doubt will be open to the public.