OpenOffice and Libre Office are both excellent office suites and can both import and export files using the Excel format. (My own choice is to use OpenOffice Calc. I've even encountered very large spreadsheet files, from a reputable academic source, that Excel refused to open but which Calc handled with ease).
However neither suite includes a DTP component. (Microsoft Office doesn't either. Publisher is an independent program). The program you need is Scribus. You can import Publisher files into it and edit them with it. However you can't export files to Publisher format - you must save them in Scribus's own format.