Not sure about Word 2007 (I'm still on 1997, sad huh!) but you can copy and paste it out of your Character Map if you have one on your PC. It's under Lucida Sans Unicode, towards the bottom.
For microsoft 2007 Go to the "Insert" tab....and on the row, you should see the Symbol button. Next to it is the equations button. Click on that. Then in the middle pane of all the mathematical symbols, scroll down and you'll see the "therefore" button.
RE:
How do you produce the 'therefore' symbol in word 2007?
The therefore symbol is the one which is three dots (one in each corner of a tryangle).