Sliding Doors Vertical Menu is a Scripts software developed by Dynamic Drive. After our trial and test, the software is proved to be official, secure and free. Here is the official description for Sliding Doors Vertical Menu:

This nicely padded vertical menu swaps between two background images depending on whether the mouse is over or out of a menu item. To ensure a perfectly Smooth transition between image change (especially in IE), it uses the Sliding Doors technique and a single background image that merges the two Backgrounds into it.