I prefer to put them 3/4 to 1\" deep.
I tested some at various planting depth fall 2010, some 1/4, some 1/2, some 3/4, some 1\" and they all had a good germination rate.
We had a extremely hot and dry July-Oct last year and when I checked mine around the first of August those that were planted shallower had expired, those planted deeper were still hanging in there.
I did my best to plant all of mine in the 3/4 - 1\" deep range this past fall.
I put together a very simple tool, a sharp shooter shovel, with pvc pipe attached to deliver the seed.
It did the job good enough. I planted around 2.5 pounds of seed with that tool this past fall.
There are a few pics of it in my \"2011 Ginseng by TNHunter\" youtube video - see my channel link below. That vid should be a the top.
www.youtube.com/yttnhunter
Good Luck !
TNhunter