What I don't understand is... "activate"? What is there to activate?
And before you ask what the plugin folder is...
C:\Program Files\Winamp\plugins
If you have a folder called Program Files and another Folder called Program Files (x86), try both of them, because it might also be:
C:\Program Files (x86)\Winamp\plugins
OR just search "Winamp" and find a folder called Winamp, and then open that, and then open the folder called "plugins". Then drag "in_vgmstream.dll" there.
Also, to activate it, you need to get a highly trained nuclear bomb disposal team, as only they can carefully maneouvre the very explosive DLL file through the very very tiny chamber and the highly radioactive "Program Files" folder, and then they have exactly 10 seconds to unlock the Winamp folder, containing the plugins folder, before the radioactivity corrupts the DLL file, which is done by two members of the team pulling down two very large handles down, at precisely the same time. Even a fraction of a millisecond out, and your entire hard drive will be erased.
Why do you think I had to get a new PC last February?
Also, the seeding will stop in a few minutes, since, unlike most of you, I'm going to bed <_<