I use c4d to do all my 3d work, have done for years, its great.
I have my units set to meters, but with the 3d printing 1m=1cm. so a cube of one cubic meter is actually one cubic cm in shapeways land.
Export your files as obj. When importing into shapeways set your units to mm. hope that's not too confusing
well thats how I do it anyway.... go nuts.