You can use the mktime() function with the pieces of your date to get what you want.
It takes six parameters. They are, in order:
hours, minutes, seconds, month, day, year. It's used like this.
echo ("December 15, 2000 is a " . date ("l", mktime(0,0,0,12,15,2000)));
You should be able to use either a split() or a substr() to parse out the pieces of your date.
Hope this helps.