Sorry, I just realized that I misread the question. The answer I provided displays all zeros as a dash, not all blank cells.
I'm afraid you're out of luck as far as formatting empty cells to display a dash.
I assume you want to do this for purely aesthetic reasons? If you just want printouts to look this way, you can select the range that will be visible on a printout, then go to Edit > Go To > Special then select Blank. Now type 0 and then [Ctrl]+{Enter].
WARNING: Do not attempt to fill all spaces with zeros because that would likely choke your system (we're talking about 256 columns X 65536 rows. That's 16,777,216 cells!)
ChrisBurch: one problem with your answer: where do you put the formula? You can't put "=IF(A1,"",0)" in A1 - that would create a circular reference. If you're trying to fill all empty spaces with a zero, why bother with a formula?
[tt]-John[/tt]
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