Copy (right click, select all, right click, copy) & paste (right click, paste) this into a text editor and edit it to your requirements. Then save it as throbber.js in a directory like c:\program files\wsh.
If you haven't already read it, please read Leigh Brasington's Netscape 4.0 Throbber Tips and Tricks before you proceed.
Don't forget to read the documentation in the file.