From Microsoft:

With Excel Viewer 2003, you can open, view, and print Excel workbooks, even if you don’t have Excel installed. You can also copy data from Excel Viewer 2003 to another program. However, you cannot edit data, save a workbook, or create a new workbook. This download is a replacement for Excel Viewer 97 and all previous Excel Viewer versions. This version is the first release on CNET Download.com