static countdown with php

hi,
how can i countdown a time by giving 2 dates?

start at: xxx pm and end at xxx am
with data and time

and them receive a result like that:
2 days and 00:00:00

i have see examples that do similiar like this using javascript but i want static "countdown" and not always runing
thanks a lot for your help :)

have a look at this:

http://us2.php.net/time

then at the first comment on that page. It gives an example of time difference between 2 times