Jonelle,
(From the reference to the C drive, I assume you're using Windows)
The most usual reason why this might not work would be simply that the plugin is not in quite the right place. Are you sure it is exactly in a folder named
C:\Program Files\Vamp Plugins
?
If it is in the right place: Does Sonic Visualiser pick up on any other plugins you install? Can you put other plugins in the same folder and check whether they show up in the Transform menu? (Try looking in Transform -> Analysis by Plugin -> submenu)
Chris