Open source means that no one company or individual have proprietary implementation on the license of the software. Depending on the site that you choose to download the software from it may be...
Open Office will happily open Excel files. You may have to play around with the formatting etc, but it will certainly import the data from an Excel spreadsheet without any problems.
Just open it as if it was an OpenOffice document. OpenOffice will read MS Works documents quite happily, and you can either save them as OpenOffice or MS Works formats.