I am using HTML5 , which works fine in Chrome and I get the calendar popup to select the date.
But in firefox it acts like
I use 6 HTML selectboxes, for the various items, with OPTION statements for the proper values:
year 2000-2050 (or whatever range you choose) month 1-12 (you can have it show month names) day 1-31 hour 0-23 (or use 12 midnight - 11 PM, this just changes the display) minute 0-59 second 0-59 (or just assume 0)
No Javascript needed, although I do use some to avoid invalid selections (like February 30). This is triggered on change of month or year.