1. Most likely, at the time the download link was created, it pointed to 4.2b (the current version at that time) and now it points to 5.1 (the current version now).
2.
http://www.kinook.com/Download/Old/U...callPro42b.exe
3. Yes, you will need to uninstall v5 before installing v4. Uninstalling never deletes any .urd files.