To convert numbers like 1, 10, 100 to 001,010, and 100 within a Microsoft Excel spreadsheet, there are a couople of ways to accomplish this.

Format–>Cells, Number tab, Choose Custom and type 000 into the short box at the right.

In Excel 2007: From the Home tab, go to Cells, select Format, then Format Cells. Go to the Number tab, from the Category drop down, select Custom. In the Type box on the right, type 000.

Other possible “solutions”.
Format(<cell>,”000″)

Resource(s)
http://www.excelforum.com/excel-general/483188-i-need-excel-to-make-1-into-001-a.html