The installing instructions are on the first page of this thread.
Basically, you just have to copy the supplied code text in a plain text file called "SongPreviewer.vbs" and put it in MediaMonkey's Scripts\Auto folder.
More information can be found in the FAQ ("How do I install scripts?"): http://faq.mediamonkey.com/index.php?ac ... artlang=en
The script is an Auto-script. That means that it will automaticly start when you start MediaMonkey, and it will add an item to the Play menu.
Depending on what you call the "right-click menu" (in the tracklist, tree or nowplaying list?), you can do the same as mentioned in my previous post, but change Menu_TbStandard
If you want the SongPreviewer in all 3 right-click menus, then make that you have 3 times the 2 lines mentioned in the previous post, and use in the first Menu_Pop_Tree, in the second Menu_Pop_TrackList and in the third Menu_Pop_NP. If you don't know how to do this, just let me know (like PM'ing me).