I'm assuming that it's the waypoint file named "mp_beach.pk3" that you've got? If so, try clicking on the file from the filebase for download -- it'll open in your browser as a bunch of gibberish -- then right click and select "save as" and you should be presented with a window where you can choose the location that you want it saved to with the default name "mp_beach.pk3. I got confused first time I tried to download a .pk3, too.
