This is the software publisher’s description.

The DOS SUBST command is a very powerful tool, even in Windows. It allows you to use a single (available) drive letter to specify a path which could be any number of folders deep, e.g. "c:\folder1\folder2\folder 3....\foldern" (it's been tested to 10 levels). Virtual Drive Creator™ (VDC) does exactly the same thing. 

Suppose you are working on a project that requires the use of a drive letter as a root directory, and all your files are in a Folder named "C:\Program Files\Microsoft Visual Studio\VB98\RPN Calc", to access your files in Explorer, or VB6 you need to traverse through the maze of folders to get there. Using VDC I chose the letter R to represent that particular path and in any explorer type directory tree the letter R is there showing me all of my Folders and files I have in that Virtual Drive. I can also access that directory from a DOS Window.

For CD users, simply copy the contents of your CD to a folder on you hard drive, not the root. Create a virtual drive pointing to that folder.  Install the CD using the virtual drive letter. And like magic you can run the CD from your hard drive. This work for about 70% of the CDs we've tested, it does not work for music CDs or Data CDs.