Here is what you can do:
Add an empty Excel file into your resources and use it as template
When your program is to save data, you can take that file from resources and save it to hard disk.
Connect to Excel file using "Microsoft.Ace.oleDb."
Save and read data in Excel just as it was a db table - there are plenty examples on the net. Google for it.
For this project you don't need Excel application on the machine.
Now, if your concern is Excel, you don't have to worry. Your clients can use OpenOffice, for example. Or, you can save data in CSV format. CSV is not Excel. You can create your own text format and your clients will be able to read it with the Notepad. You can do HTML/XML combination and have your html page load whatever xml you supply.
Seriously, create a spreadsheet and tell your clients that they can open it with their favorite spreadsheet editor.