I have ran into that same problem. I actually developed my using server side programming, but I did a quick search to try and help you out and found this.
Seems alright, didn't look at the source too much, but seems to be purely JavaScript.
Take look:
http://www.rainforestnet.com/datetimepicker/datetimepicker.htm
Here is the demo page link:
http://www.rainforestnet.com/datetimepicker/datetimepicker-demo.htm
good luck
