Re: how far south of the equator, is the sun at the winter solstice

The short answer is The Tropic of Capricorn; or -23d 27' latitude (that's minus 23 degrees, 27 minutes).
Conversely, +23d 27' latitude is the Tropic of Cancer, and represents the Sun's declination on the Summer Solstice.

For a more involved answer, with a cool quicktime movie, please see Eric Weisstein's Treasure Trove of Astronomy on the Winter Solstice.

Thanks for using Mad Scientist,
Joe