OK, this works in NX 3 and 4, but I just discovered that it's broken in NX 5 (I've opened a PR).
You first need to do a little pre-setup. Take you model and rotate it around until you're looking normal to the desired 'projected area' (make sure that you have turned OFF perspective display). Now go to Format -> WCS -> Orient... and select the 'CSYS of Current View' option.
Next go into Preferences -> Visualization... and select the Visual tab and then the tab labeled 'Edge Display' and then change the Hidden Edges option to 'Invisible' and hit OK.
Now go to Insert -> Curve from Bodies -> Extract... and select the 'Shadow Outline' button. As soon as you select the button the function executes and usually you will not see anything change on the screen, but if you now Hide (Blank) the solid body you will see a 'Shadow Outline' of the body. Note that these are 3D curves extracted from the solid, based on the visisble 'outer profile' or 'Shadow Outline' of the solid.
The last step if you're looking for a 2D representation of this 'Shadow Outline' is to go to Insert -> Curve from Curves -> Project... and select the Curves and and then for the plane of the projection, under 'Plane Method' select 'Set to XY Plane' and then hit OK.
You now have the 2D 'projected area' of your original model.
John R. Baker, P.E.
Product 'Evangelist'
NX Product Line
SIEMENS PLM Software Inc.
Cypress, CA