Membership Plus Deluxe supports Windows 8, but it is true just for version 12 which is not available for sale anymore. Version 6, which you have, is not compatible with modern operating systems. Instead, the company released the next version of Membership Plus called Realm. Realm is available for purchasing and it's compatible with most of the Windows operating systems including Windows 8 or Windows 8.1.
For more information access the official website: http://www.memplushome.com/product#