Thank you very much!

But, at about what temperature should he be in? I think I read somewhere that placing them anywhere below freezing is bad, but they hibernate in temps like that in the wild (group brumation?). While you're at it, when should I take him out again in spring?
I'm so glad the info was welcomed. For a North American species, I like room temp with a small 100 degree basking spot on one end of the cage. A little 50watt spot light usually acomplishes this. I put the light on a timer for 14 hours during the summer months and shorten it according to the season until hibernation.
During hibernation, I've had the best results around 55degrees. Too warm and they'll metabolize their fat stores too quickly. Too cold and they don't wake up...ever. Remeber, even in the dead of winter in Vermont, for example, no matter what the above ground temp is, its anywhere from 50-65 underground where the reptile hibernation burrows are. I can tell you from tragic personal experience that if you let them get too cold they will die.
I usually start gradually letting them warm up when the weather starts getting warmer in Spring. They usually do this naturally, unless you have them in some sort of artificially controlled device. I used to use old refridgerators laid on their back. Not plugged in, of course. When I see them up and moving, I'll give them a soak in very shallow, room temp water every couple of days. After a few days up, I'll click on the basking light and give them the opportunity to bask. Once I see regular basking, or they just seem to hang out on the warm side of the cage for a few days, I'll offer food.
Also remember, these are generalities, as I don't know your species very well. Its been my experience that these techniques and temps work well for most North American reptiles from temperate areas. Hope this is what you were looking for. Good luck.