it is better to translate as:
To my surprise, he dares NOT to tell me this thing !
dare not is not "不敢", but "敢不". You shall not translate it into Chinese, but just take it as is. If you have trouble to accept it, keep using it for a while, it will sink into your brain, and you will no longer question whether it is "不敢", or "敢不". As you already know Chinese, you certainly can understand the different between "不敢" (don't dare) and "敢不" (dare not). In a word, "dare" functions like (but not quite the same) "do" or "can", when it uses as "dare not", as to "do not", or "can not". If you want to use "dare" for "不敢", then you shall say "don't dare".
I cannot type in Chinese, I hope you can understand my English explanation.
2011-11-03 22:32:12 補充：
"dare" is just a regular verb, however, sometimes, it behaves like "do", as in
2011-11-03 22:34:51 補充：
If you want to form a question with dare, you need "do, can" to accomplish.
Don't you dare to follow my order?
try to get a feeling the difference with
You dare not follow my order.
2011-11-03 22:38:55 補充：
Dare can NOT be auxiliary verb (助動詞). Its conjugation is: dare, dared, dared.
2011-11-03 22:44:05 補充：
I make a mistake
It shall be
Don't you dare follow my order.
"...he dares NOT tell me this thing." (in my answer)
2011-11-03 22:45:30 補充：
The reason is like I say, "dare" is not an auxiliary verb, but sometimes it behaves like one. It will not need "to" to follow a verb. The above examples is the case.
2011-11-05 00:23:16 補充：
Everything is correct, except:
dare not (to) pay attention --> you don't need "to"
Dare you fight with him --> shall be "do you dare fight with him".
2011-11-05 00:25:31 補充：
"Dare" need auxiliary verb like "do" to construct a question. Even though SOMETIMES it behaves like an auxiliary verb. For example:
You dare not watch a ghost movie.
2011-11-05 00:27:09 補充：
The reason is, if you use
You don't dare watch a ghost movie
it changes the meaning. I think you know the difference between "don't dare" and "dare not".