Is there a way to open a Microsoft Works file without downloading a file-opening program? Can anything in MS Office do it?
Microsoft Office does not have native support for Microsoft Works. Microsoft Works was discontinued in 2007 and they dropped support for it.
There is a Microsoft Works 6–9 File Converter available for download. Im a bit surprised looking at the supported OSs and Office versions - it is very limited, but it might still work for you on a newer OS/Office version.
Microsoft Office Word should be able to open newer Works Word Processor files by default. You can use the "Works 6 - 9 Document (*.wps)" file filter in the open dialog.
Microsoft Office Excel is a bit trickier. You won't be able to choose a file filter, but choosing "All files" and selecting a Works .xlr file should work fine, since the new version of Works Spreadsheet uses the same format as Excel.
Unfortunately, you're probably out of luck for Database, Calendar, and Portfolio. New Office applications lack compatibility with their formats. Furthermore, if you need to open files created with a very old version of Works, you probably won't be able to. There are some add-ins for Office for compatibility for some of the older formats, but none will offer you a complete solution.
Your best bet is to download a converter program for these.