OK, just stumbled on this post but..
(isn't that one of the cool things about SP?)
I am not a sweat-er, either.
I drink PLENTY of water,
I am not mal-nourished (far from it),
I get my heart rate up to 120-160 for 60 minutes most days
(I do interval training on a treadmill or the elliptical)
I asked my doc why I don't sweat and he said it's really about how many sweat glands you have per square inch of skin.
I do sweat, but barely.
I can wear the same clothes to the gym like 3 days in a row (except for my bra- oh, sorry- TMI??)