In the VDL Readme 7.0a PDF, on page 8, I list the various scenarios of using Kontakt Player within Sibelius. Let's see if I can cover where to get what.
Sibelius 7I recommend using Kontakt Player 5 for use of VDL in Sibelius 7. And hopefully you're running it in 64-bit mode. If not, that's OK too. KP5 can be downloaded for free from the
Native Instruments site.
Sibelius 6Since Sib 6 won't correctly see KP5, you'll want to run Kontakt Player 4. If you're already using it, great!. If not, then you can still request it
here.
Sibelius 5If you have followed the instructions in the Readme and have updated your VDL library version to 2.5.2, then you will already be running the Kontakt Player 2 version that you'll want to be. (Due to the incompatibilities between KP4/5 and Sibelius 5, you'll have to stick with VDL 2.5.2 until you are able to run Sibelius 6 or higher.)
Late
Hugh