Answer: You will have to add a tab to the ribbon and then add the check box from there. In previous versions of Word you used insert special characters to insert a check box.
Check boxes are nice in Word documents you have people filling out and returning and to let them just click on a box to show it checked.
To do this in Word 2007 go to the Word button on the top left of the screen. Click Word Options button at the bottom of the box. Check the Show Developer Tab in the Ribbon and press OK.
Make sure your insertion point (the place typing will start at) is where you want the check box inserted. The Developer tab shows on the right above the ribbon and is a separate ribbon. Click on the Developer tab. In the Controls section of the ribbon click the Legacy Tools button (hovering over buttons gives Tool Tips with the name of the button). It is the 4th button on the second row in controls in my Word 2007. Then under Legacy Forms click the check box button. The check box will appear at your insertion point.
This process will also work to insert drop down boxes and radio buttons (called Option Buttons under ActiveX instead of Legacy).