Take your data file and rename it with a .txt extension (the Mach3 3d plugin leaves off the .txt extension!)
Then in Rhino just Open>File and scroll down to the file type "Points File (.....*.txt) and select that.
Rhino will display your point cloud as a web of dots.
Rhino needs the .txt extension to see your data file.
That much I found out yesterday!
LionelB in Durban, S.Africa