This is a tough one for me since I'm not an Attorney. First, you need to get very good documentation from the folks that did the pressurization tests. At the SAME time, get yourself a notebook and date and document when, who, HOW, and what you talked about regarding the problem. SHOULD you go to court, you'll need to prove to the judge that you tried to rectify the problem in good faith AND that you had tests. This step is very, VERY important!
Now, who do you go after ... In my non-expert opinion, you have to ask if the carpet layers should know that the house is tight before they lay the carpet. At the same time, you have to ask yourself if the builder should REALIZE the house he built is tight and he has to 'adapt' the house accordingly. In my opinion, I think the builder needs to fix the 'leaks' AND replace the carpet. I have one question: If the carpeting can be easily removed from a 'spot' where you get the ghosting, can a 'white sheet' (or filter, of sorts) be put in its place to see if the ghosting continues??? In theory, you should see the ghosting. If you can have the carpet pulled away from one of the ghosted areas, 'prop' up the carpet and lay a white sheet there. Since it should be 'easier' for the HVAC system to draw at that spot, you should get what you'd expect! See what I mean??? Just make sure that you don't affect any other 'ghosted area' above or below or next-to the one you're using as a guinea pig. (For example, if you're testing this on a stair-tread, make sure the carpet is in place on the tread ABOVE and BELOW the one you're testing. If not, you will have created a 'leak'. Again, see what I mean???)
Other than that, I'll see if I can get a legal expert to guide you. My best to ya and hope this helps. Remember, if you have to go to court, keep EXCELLENT records of your calls and conversations w/whoever!!!