In order to allow web access to a different directory outside the root directory, you need to give Apache access to the directory, and then use the Alias directive. The Alias directive will map any directory into the web root.
For example if you want to create a virtual directory called test, and the directory is in the D:/example/test, then modify your httpd.conf and add the following entry at the bottom of the file:
<Directory "D:/example/test/"> Options Indexes AllowOverride all Order Allow,Deny Allow from all </Directory> Alias /test D:/example/test
On a typical Windows installation, the httpd.conf file is usually located in the following directory:
C:\Program Files\Apache Software Foundation\Apache2.2\conf\httpd.conf
So if a file file.htm exists in D:/example/test, the URL of the resource is:
http://www.example.com/test/file.html
and it will be served from:
D:/example/test/file.html
For more information visit the Apache HTTP Server Version 2.2 documentation.