Create a simple word maniulation script

We need a simple PHP script written: It will allow the end user to put in a couple of words in a few different fields. It will then attempt to use the letters from those words to come up with new words that match a preset word list. The user will decide how man words they want to generate from the new list. It will then sort them based off of how many of the letters are used in the new words. The script should also attempt to put words together as a whole. For example. One word that was put in was watch, another was dog. It would generate watchdog (if that was on the list). This is the initial start of a project. If things work well, we would want this developed even more. The interface should be a simple but pleasant interface. Preferably using ajax or the like, so the page does not need to refresh itself. Rather once they click calculate the bottom will change. Or if they switch the amount of words.