Can I use Kontakt 4 instead of KontaktPlayer 4? Or are these the same thing?

I'm having trouble with getting the VDL SoundSet 6.0 to appear in the active devices drop down menu for Kontakt 4.
Thanks

They're the same software. Kontakt Player is essentially ONLY useable for Kontakt Player libraries, and won't work for editing libraries or loading non-player libraries (which require the full version of Kontakt). Kontakt is basically just an unlocked version of Kontakt Player.

In either case, you'll probably see it appear simply as ";Kontakt 4"; in any of your host applications - regardless of whether your using the full or player version.

If you're having trouble with your VDL Sibelius SoundSet not appearing, the xml file that came with your Sibelius template may not have been placed into the correct location. Check the documentation that came with your template (assuming you're using a template from The Write Score), or get in touch with their helpful support team at http://www.thewritescore.com.