This is one of those yes and no answers. A lot depends upon your local BATF agent. Not sure about that particular setup but the general rule is that you can own the non-registered parts or the full-auto parts as long as you don't own the firearm. an example would be if you owned an AR15 - style firearm and kept it in your domicile, you could not legally have an M16 bolt on the premises without the appropriate tax stamp. There are also exceptions to this.
Also the STen kits that were recently widely available are legal as long as you don't have any tubing of certain diameters, this of course depends upon the BATF. If you live outside of United States jurisdiction these don't apply to you, of course.