I've seen it explained as below:
Ganged = dual channel mode for ram. All cores get access to 100% of the ram.
Unganged = single channel. Each core gets access to a stick of ram. In theory, the unganged mode is better as each core will get access to data quicker. Also, it also allow you to control the clocks independently from each other.
I would run unganged for an AMD build, as it seems to run better from my experience.Edit
: Here is a nice article on this topic for your review and enjoyment http://www.ilsistemista.net/index.php/hardware-analysis/3-the-phenom-phenomii-memory-controller-and-the-ganged-vs-unganged-question.html End of Edit
On PAE, here is a nice article about it for your review: http://en.wikipedia.org/wiki/Physical_Address_Extension
The thing I would take out of the article is the concern of stability by making your "32-bit system" into a "64-bit system". I would recommend against it. If this is something you truly want, I would do a Google search on how to or hopefully a member will post you directions on how to do it.