The first step shown in m@dhu#s answer is correct: convert the string you get from the aspxpage to a DateTime value. But then, use a parameterized query to get the data into your database! By string concatenation, you would open it for SQL injection attacks.
Do you know how such an attack works? Well, read a thread in the hall of shame: http://www.codeproject.com/Feature/WeirdAndWonderful.aspx?msg=4335687#xx4335687xx
] (the information on the injection attack comes late - and: they haven't fixed it yet, you can try your skills...)