Next you need to download VAG-COM 409.1 from the Ross-Tech website:
www.ross-tech.com/vag-com/download/archives.html
(Use the link for version 409.1 - shown as 'For MODERN SERIAL Interfaces')
Save the file to your computer, then run it.
When installing VAG-COM on Windows 7, it is important that you do NOT install it within the 'Program Files' folder. Windows 7 protects this folder and prevents programs from writing files into it, which would prevent VAG-COM from working.
So when you see the screen showing the location for installation, change it to another folder, e.g. C:\Ross-Tech\VAG-COM: