If you want cells to be blank when a formula = 0 you can change a setting in
Excel 2007, just select Excel Options>Advanced and uncheck the "Show a Zero
in Cells That Have Zero Value" checkbox. If you have Excel 2003 I think its
under Edit>Options or Tools>Options, I can't remember.
If you just want that particular cell to be blank when its summed to 0 then
use Rick's or FSt1's formula.
Hope this helps! If so, click "YES" below.