First of all, latest versions of Microsoft Word (since version 2010) actually support documents (.wps) from Microsoft Works and can simply open these documents and re-save to other formats, including .doc files-
If you only have access to some previous version of Microsoft Office, you will have to download and install special Microsoft Works 6-9 File Converter that acts as plugin and allows users to open and work with Microsoft Works documents.
Open source word processors such as LibreOffice Writer or OpenOffice.org Write also may still support Microsoft Works formats and thus achieve wps to doc conversion, either directly or through some middle format.
A viable alternative presents itself in 3rd party document converters like the ABC Amber Text Converter, so these utilities may be worth a shot if you have trouble convert wps to doc.
Last option would be to get your hands on some old version of Works. It was commonly bundled together with laptops and new computers so you may have some old Works installation CD. Works allows users saving documents either as .rtf or .doc file, which is all you need.
Updated: March 28, 2017