open Works .wss files in Excel... but they can be saved, using works, as Excel, .xls files, which can then be opened in Excel.
Works will open Excel files, but if the excel file has more than 1 sheet you get asked whic sheet you want to open, as works spreadsheet cam't handle multiple sheets.
If you dont have Excel, but you want to open an Excel file just to "read" it, i.e. not to edit it in any way, you can open it with the Excel viewer which is a free download from Microsoft. click here
If you do need to edit it, and it's more than 1 sheet, you can try using the spreadsheet in OpenOffice, click here which handles Excel very well, (apart from Macros)