You can do it (but you won't want to!) by:

Creating a new workbook.

Change the normal style for numbers to be currency.
In xl2003 menus:
Format|style|select Normal|Modify
and change to the number format you want.

Save it as a template named book.xlt (.xltx or .xltm in xl2007???) and store it
in your XLStart folder.

xl2003 and below will use that template workbook when you create a new workbook
by clicking on the new icon on the standard toolbar.

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The reason you won't want to use this is the way it treats any numeric
entry--even dates and times.

TripG wrote:

I want the default number of decimal places to be three when I create a new
spreadsheet. I'm using Excel 2007. I sent a spreadsheet to a colleague with a
column formatted to 3 decimal places, but is was set to 2 decimal places when
he opened it on his computer.

--

Dave Peterson