Edited 30/07/05: if your reading this stop now and read the pinned article in the planted section. it's much more informative and i have now learnt the riccia does not need to be matted, in fact works better if it isn't.
now come on all thats needed is about 30 mins of time, some cotton thread and a lump of bogwood.
the riccia needs to be matted together first. if it's all loose bits make a loop of air tubing (poke one end into the other).
put your floating loop in the tank (floating fence)
dump the bits of riccia into the loop and leave it for about 2 weeks and dont touch it at all.
after 2 weeks you'll have a matted mass of moss.
take this slab of riccia out of the tank very gently, lay it on a piece of bogwood and wrap cotton thread (preferably green) around it tightly enough to hold it in place but not so tight as to cut into the plant.
then tie off the end of the thread and submerge your new riccia coated log.
this pic was taken immediatly after making the back log, (all the riccia on the back log grew from the "carpet" in front of it) you can then repeat the cycle after about a month as when riccia grows bits float off to the surface, put back in the loop and so on...
much more rewarding than chucking a stem plant in the gravel and looks great as well