PWM (Pulse-Width Modulation) is a method of generating an analog output from a digital output pin. There are no "PWM inputs", it just doesn't make sense to say that.
Maybe something like this:http://www.sparkfun.com/commerce/product_info.php?products_id=8680
How does that thing actually work?
... you have to put a high value pull up or pull down resistor on the input to define the value un-pushed