If you have another computer, you can download NPE on that, then put it on a flash drive and run it from that on the problem system.
One caution, Be careful if/when NPE suggests removing any files or settings. If you do not understand what they are, you may leave your system unbootable. You can post the recommended deletions in the appropriate board for your Norton product, Norton Internet Security or Norton 360 to get advise on whether it is safe to remove those entries.
If you believe you have an infection, a better solution might be to go to one of the free Malware Removal sites below. They have expert malware removalists that will guide you through diagnosing and fixing what is wrong with your system.
http://www.bleepingcomputer.com/
http://www.geekstogo.com/forum/
http://www.cybertechhelp.com/forums/
http://forums.whatthetech.com/