A useful website for you:
http://www.chambersha...ards/wwizards.py/main
Click in the search box to open it then type in your known letters and use ? for unknown ones, just as you did in your post. Click on Search.
If you get "No words found" try changing one of your known letters for a ? and try again.
It also works for anagrams. Just type in the letters in any order and click on search and it will unscramble them for you.