In reply to JB:
The lonely planet patagonian andes guide is good enough for a trekking holiday.
When I was there (march / april) there were no crowds (and fabulous sunny, wind free weather) in Fitzroy / Paine. Best trekking I've ever done.
Flew into Rio Gallegos, Moreno Glacier, Fitzroy, Torres del Paine, Puerto Natales, Punta Arenas, Ushuaia.