Take a look at the date() and mktime() functions. Personally, I DETEST translating date formats around between PHP and whatever database I happen to be using.
Instead, I store all dates in the DB as an integer, and use date() and mktime() to derive/retrieve the values to save/get. This gives me a completely standard way of storing this information and complete flexibility in how I decide to display this information.
Hope this helps.
-Ben