As far as I know, it will not reduce muscle soreness if you stretch before, but will help if you stretch during and after. I wouldnt bother to stretch too much before your workout, it won't do much for you.
Stretch the bodypart you are training as soon as you are done...do not stretch it before.
*NATURAL PRO BODYBUILDER *MONTHLY COLUMNIST FOR PLANET MUSCLE, NATURAL MUSCLE AND IRONMAN MAGAZINES
*CEO OF BROSERBUILT.COM
*PIONEER OF POWER/REP RANGE/SHOCK AND FIBER DAMAGE/FIBER SATURATION TRAINING PROTOCOLS