Use PVC elbows to make a rectangle that is
slightly larger than your bed. Paint or stain the dowel
rods to match decor. Hang the rods from the ceiling at each
corner and drape the muslin onto the rods. Alternatively,
you can see loops at the top and put the fabric on before
hanging the frame.
You can stencil or dye the muslin
however you want. You can also make matching tiebacks for
the "four posters" or use raffia and silk flowers
for the tiebacks.