If you want live sphagnum moss, all you need to do is take a bag of dried moss, line the bottom of a clear container (like a tank or tub), some pour water over it to get it nice and wet, put it under light or in sun (but don't let it get real hot or it will fry) and...wait. Don't let the moss dry out. The dead moss will regenerate. This takes some time...weeks to months. But I have always put a layer of dried LFS on the bottom of my tanks (just to increase humidity) and it always starts growing and turns into a thick carpet of live moss after a while.
Since it regenerates from the top layer, a broader, thinner layer of dead moss will net you more moss. If its in a jar, you will only get what will grow from the top (maybe sides if its clear and gets good light).
Hope that helps. [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile.gif[/img]