You can write data to a CSV/TSV file which Excel can use or have linked into an XLS.
There are several examples of 'Component-Reporters'...
You can then read this 'text' back in and convert it to numbers etc as desired...
On Windows you can access Excel directly using... require 'win32ole.so' which you must install.
This then allows you to read/write XLS files directly...
There are good www resources to help you - here's an example http://davidsulc.com/blog/2011/03/27/win32ole-and-ruby-working-with-worksheets/