I've used MP3 Tag, same version and am using Win 7 64 bit and WMP12.
When you have looked up the album art and the title tracks you need to also rename the filename. Under the menu list are a row of icons. The best one to use I find is the "Tag - Filename" icon (red dot on top with arrow pointing to a page). When you click that it opens a window and allows you to select the format(I use %title%-%artist%) wich then names the file "trackname - artist.mp3".
This should then be sufficient for WMP to update the tags. The best way I found was to delete all the tracks from WMP (library only) and then let it refind all the tracks if you have lots to do.
Hope that helps:)