As of March 2006, you cannot travel independently in Libya. You must work with a tour company on an itinerary while you are traveling in the country. The tour company will take care of arranging your visa with the Libyan government.
This does not, however, mean you are confined to tourist areas. The tour companies are fairly liberal with where you choose to go. You can arrange for a Libya tour company to take you to Tripoli for a few weeks, or you can arrange for a tour company to help you with a visa as you drive your overland vehicle across the Sahara.