You need to save as a .doc document, if you want the receiver to be able to open and edit within MS Word.
Niel actually you can open and view a .pages document on Windows PC if it has a PDF reader installed.
.pages saves as a container (Zip flie) with a viewable .pdf in it. You right click on the file in Windows explorer and you see the .pdf file. Click on that and it opens in your PDF reader (Likely thats Adobe Acrobat) for viewing. There are several other files inside as well.
This is little documented for some reason