I have a section of my back yard just outside DC that is what you describe -- planted to moss, with ephemerals popping through, and edged by opiphigion (dwarf mondo grass) -- the mondo grass can take foot traffic better than the moss can, but likes the same dappled-sun-poor-sour-soil environment, so I laid it in where we tend to walk. I started with a small amount of moss that I spread by means of a technique I learned on the GardenWeb forums -- I bought a cheap blender at a thrift store, and threw a heaping cup of shreddded moss in along with a quart of plain yogurt that was a bit past its prime. Whirl it up, and thin the resulting mess down with another quart of lukewarm water -- spread that out on bare sandy soil (I dipped it up in a perforated serving spoon, then tapped the handle to disperse the droplets) and in about a week you'll see the moss start to sprout. I did this with the flat velvety kind of moss -- not sure how it would work with thes stuff that looks like tiny pine trees.
It is NOT the lowest-maintenance section of my garden -- it takes a lot of weeding and in the fall I lay down bird-netting so I can flip off the leaves without having to rake the delicate hummocks.
Here is a FAQ on growing moss from the GardenWeb Moss & Ferns forum: