To elaborate what zdog has said, this returns data identified as Excel data to the client. What the client does with it is completely outside the control of the CGI, as it should be. For example, if this is returned to IE on WinXP, this may open an Excel window within the browser, but only if configured appropriately. When returned to Mozilla on WinXP, it will ask you if you want to Save or Open, at which point Excel is one of the choices. When returned to Galeon on Linux, it will ask for Save or Open, and OpenOffice (if installed) may be one of the choices.

In other words, your script returns some data. The client does what it wants with it. That codes does NOT creates an Excel-window where you can use the all the Excel-abilities!.