Have you checked out Petranka's Salamanders of North America? This will give you lots of info. By the way, most herpetologists currently consider the three-lined salamander to be a different (but closely related) species from the longtail salamander. The longtail group consists of:
Eurycea longicauda longicauda (Longtail Salamander)
Eurycea longicauda melanopleura (Darksided Salamander)
Eurycea guttolineata (Three-lined Salamander)
My experience is mostly with E. longicauda longicauda. In lowland areas it is most often found in rocky, spring-fed streams, and is also common in cave entrances along with E. lucifuga. In the Appalachians it is found in a wider range of streams. Adults can be found both in the streams and a fair distance away in moist woods. E. guttolineata in upland areas uses the same habitats as E. l. longicauda, but in lowland areas will use sandy or muddy streams and even swamps and ponds (E. l. longicauda is never found in these habitats). From what I have read of E. l. melanopleura, it is more like E. l. longicauda, and does not use swampy habitats like E. guttolineata.
Presumably E. guttolineata is more heat-tolerant than the other two, just based on habitat and range. Otherwise captive care should be similar. Keep them cool and damp, give them plenty of hiding places, and feed them small inverts. Flightless fruit flies and pinhead crickets are ideal. If you have open water in the cage, you could also feed them amphipods (scuds) and isopods.
Besides other Eurycea species, the salamanders most similar to longtails in habits and habitat are the dusky salamanders (Desmognathus species). You are also likely to find red, mud, and spring salamanders with them. Look for small streams in wooded areas. Streams with fish usually have fewer salamanders, so if you see a bunch of fish swimming around, go further upstream. Salamanders can usually be found under flat stones, logs, or leaf packs near the water's edge. An ideal cover object is one that is resting lightly on the ground (not embedded), with one end in the water and one end on land. Larvae will be under similar objects out in the stream.
The best way to get a good eye for salamander habitat, and to learn how to catch and field ID them, is to go out with someone more experienced. I suggest you try calling a herpetologist at a local university and asking to go along on one of his field trips. Nature center staff, state park biologists, nongame biologists with the state DNR or Fish and Game program, and local herp clubs are also good places to find more experienced people to show you the ropes.
Always check your local laws before you take anything home, and be sure you know what it is. North Carolina has a lot of salamander diversity, and there may be rare and protected species in your area.