Insofar as whatever portion of the muscle soreness is related to inflammation, the anti-inflammatory properties of omega 3 from the fish oil and metabolic conversion of the lipids in the flax oil (it’s my understanding flax oil doesn’t actually contain omega 3 as such) would help reduce it. As would other dietary anti-inflammatories, such as ginger, turmeric, etc. These really are just a part of the proper nutrition Kevin mentions. I suspect the unknown supplement being referred to is hyaluronic acid. Just Google it, you’ll find plenty of info on it.
As far as external physical methods, check out this link offered by Irishdazza in another thread.
http://www.t-nation.com/readTopic.do?id=551 687
Much of the above applies to specific injury as well as to ordinary soreness.