I would like to make it south to Luxor and Awsan for about 4 days to check out the area. Is it possible for me to take a train or flight down there, and then sign up for tours while I am down there?
Yes to all.
Take the overnight sleeper train to Aswan, you should be able to buy the tickets at Ramses train station in Cairo. There is a luxury train just for tourists, it costs around 60 USD to get to Aswan from Cairo. Totally worth the money. You have to pay cash in EUR or USD. Check out www.seat61.com for more info on trains in Egypt.
You can arrange tours in Luxor and Aswan with your hotel in Luxor or Aswan. It is not worth it to book these tours in Cairo, all you do is pay more because the travel agency in Cairo wants a cut too.
A typical tour from Aswan is the tour to Abu Simbel, it costs around 15 USD without the entry fees if you go in a small minibus. Most backpacker hangouts can arrange this tour. You need to inform them about 1-2 days in advance, so if you are on a tight schedule I recommend that you book your hotel in Aswan through a booking engine like hostelbookers or hostelworld (or the accomodation link on this website) and then call the hotel and ask them to arrange for the tour.
Tours from Aswan leave around 3 am and you have to pay by 3 pm the day before. Ask for the long tour that includes Philae Island.
There are similar day tours around Luxor, also easily arranged with your hotel, but when I was there I found it to be better to do my own thing. To see the Valley of the Kings and all the other sights on that side of the Nile I took the ferry and then rented a bicycle.
From Aswan you need to take the train to Luxor. Tourists are not allowed to use the bus to get in and out of Luxor. From Luxor I recommend taking the luxury overnight sleeper train back to Cairo. Alternatively go by bus to Hurghada (possible with a few tricks) and take the ferry to Sharm and continue from there to Dahab. Although if you wanted to dive you could just as easy do this in Hurghada.
Egypt is a backpacker's paradise, as long as you got a decent guidebook (Lonely Planet Egypt is standard) travelling around the country is very easy.
You can pick up the LP Egypt in some bookstores in Cairo and in many bookstores in Luxor.
[ Edit: Edited on 18-Aug-2009, at 11:00 by t_maia ]