This seriously isn't a DIY job, especially if you want to keep your iPod's warrantee. If you live near an Apple Store, take it in and see what they have to say about it. It's difficult to say whether you'll get a repair/replacement without seeing it first. My guess is that they'll just tell you to live with it. 🙁
Just out of interest, how could dust have got behind the screen from opening the package?