Blankety blank, blankety blank...

To make a cell blank when zero in Excel you could do so via conditional formatting, setting the font colour to be the same as the background colour when it equals zero.

This technique is a bit limited however, and hits problems if you need to use other conditional formatting or when the background colour varies from cell to cell.

Another more flexible method is to use the following formatting string for your cell.
Just go to Format > Cells > Custom and plonk it in to the Type box.

0;-0;;@

The above format doesn't show a thousands delimiter. To get that in use: -

#,##0;-0;;@

Why Microsoft made this expression so bloody complex I'll never know. But hey, Microsoft are Microsoft, they'd make the complete works of Shakespeare out of a crisis.

Have a play with varients of this for other effects.

Enjoy!