You have some options. If you run on Windows you can use COM to read data from an Excel file.
If you run on *nix, Mac or other than you need to read binary Excel file or export data to csv in Excel and read it by php script.
To read csv file search the forums - there is some complete solutions.
To read binary Excel file you can use free class at sourceforge (a little buggy), or commercial solution http://www.eephp.com/