It is an Microsoft Excel spreadsheet file. If you don't have MS Excel, you should be able to view/modify the file with Open Office: http://www.openoffice.org/
Open up OpenOffice Calc (that's the spreadsheet module). Go to File > Open. Navigate to the location where you save the xls, select it and open it. Fill it out and hit save. OpenOffice will ask you if you are sure you want to save to a non-native format. Click yes. There you go! Email the file to the appropriate location, and you're done!