This question came up on another thread not long ago, you may want to look for it.
I try to put more pressure on my fingertips and less on the heel of my palm when it starts to feel like there is too much pressure in my wrists. Also putting more weight in your heels, even if they don't reach the ground can take some pressure/weight off your hands.
You could also try dolphin pose, which is similar to down dog, but on your forearms rather than your hands. www.yogajournal.com/poses/2462
highest weight ever:202, SP starting weight: 143
New goal: 125 lbs, just to see what that looks and feels like! Hit it: Feb 2013!
H: 5''4" 49 y.o.
"Don''t let yesterday use up too much of today." Will Rogers
"Eat Food, Not Too Much, Mostly Plants" Michael Pollan
| current weight: 8.6 over