It's a little more involved in Word 2007. With the table selected, select
the Layout tab of the Table Tools and click on Formula. If you have values
in the cells above, then SUM(ABOVE) will be offered as the default formula.
Otherwise you have to choose a function and type in cell references.
The same is true of the Sum button, which you can add to the QAT (it's in
the All Commands section Word Options | Customize).

Signature
Suzanne S. Barnhill
Microsoft MVP (Word)
Words into Type
Fairhope, Alabama USA
> In older versions of Word, I was able to add (sum) a simple column of
> numbers
> by inserting a formula rather than using Excel. This was especially
> useful
> when preparing a letter or other document.