I have a 325i with SMG also...not quite sure what your question is...
From what I understand, the sport button is just a different program, that will make your SMG shift faster.
There is also a "launch" mode, similar to the SMG II of the M3...where you would have to push the DSC button for about 3 seconds, and push the sport button. AFter that, it is pedal to the metal (carpert)...and it should launch your car, the fastest possible way, and shift the fastest possible way....
Haven't tried it myself, because I haven't reached 2000 KMS yet...but can't wait!