Using Excel 2003, I am able to define the column as text, enter the number with leading zeros, and then use it elsewhere in the spreadsheet as if it were a number.
For example, column A is defined as text. In cell A1 I type 00023, and because it is a text cell the zeros are not dropped.
Cell B1 contains the formula =A1 * 2, and displays as 46 (2 times 23).
Probably works the same way in Excel 2010, but I don't have 2010 on this computer, so I can't say for sure.
Edit: Oops. I see lsayre already gave the same answer while I was researching.