Some updated information (May 2013)
South Node is always in exact opposition to the North Node. See:
https://en.wikipedia.org/wiki/Lunar_node
Astro.com will compute the South Node. There, it is called the "Descending Node". You can find it in the "Extended Chart Selection", in the section of checkboxes with things like "Always use True Node" "Always use Mean Node".
You can also opt to draw the aspect lines. If you don't, you can still get the information in the table. Sometimes, the lunar node aspect lines will give a better overall picture of the karmic winds you are riding.
Finally, if you (or rather, anyone curious about this subject) have not yet, check out
Karmic Astrology, Volume 1: The Moon's Node and Reincarnation by Martin Schulman. I have the fortune of glimpsing fragments of my past life experiences, and the book's description is both accurate and helpful. When I read the description for mine's, I felt like I was being stabbed with (uncomfortable, yet piercing) insights every other sentence. When I showed my some of my friends their passage, they also felt the same though they might not have direct past life recollections.
There's also a section on aspects to the Lunar Nodes. The only ones that matter are: conjunction for one (since it would mean an opposition to the other), conjunctions for both, mutual reception, squares (a square for one will always square the other), and trine for one (since that would mean sextile to the other).
When combined with Stephen Arroyo, et. al.'s work with psychological astrology and various meditative (transmutation) practices, this gives a lot of good guidance on what you need to be working on. Good luck