Here's a little somethin'...
http://upload.wikimedia.org/wikipedi...s_bow_grip.jpg
The photo's angle is a little weird, but it shows that the thumb is tucked under, and very stress-free. The fingers would be sort of evenly draped over the top of the stick. Make sure that your pinky finger isn't hyperextended towards the bow screw. Everything should be loose and relaxed.
The term "bow grip" is a misnomer. It's more of a hold. If you're gripping the bow, you'll get pain at some point.