Old formats from Microsoft Works are rarely supported in modern programs, and quite frankly, most programs do not support it. Your best bet is to find installation of Works, either on internet or on CD bundled with older laptops etc. and export your document to some common exchange format like CSV, RTF or similar.
However some programs like Kingsoft Office for example, claim that they support .wps files and can work with them and possibly export them to something else, hence a WPS to XLS conversion would be possible.