For setting up the virtual host on window system below are the steps -

Lets suppose,

http://localhost will access for all the projects in a file,

http://qa11.localhost is for access to only one project and also it will set the document_path for that public folder.

Note : Please note that you have to take backup of files, before doing any update there on file to avoid any issue in future.

Now Following are the simple steps :-

Step1 ) Firstly inform the system, what to do when you called http://qa11.localhost

FilePath: C:\Windows\System32\drivers\etc\hosts

Add the Following line , in top of file

127.0.0.1   localhost
127.0.0.1   zf11.localhost

Step2 ) Inform the apache, to include this extra file.

FilePath: C:\wamp\bin\apache\Apache2.2.17\conf\http.conf

Now uncomment the following line

Include conf/extra/httpd-vhosts.conf

Step3 ) Inform the apache, what we have to do when request come from http://qa11.localhost

FilePath: C:\wamp\bin\apache\Apache2.2.17\conf\extra\conf\extra\httpd-vhosts.conf

Now add the following line, at the end of file

<VirtualHost *:80>
    DocumentRoot "C:/wamp/www/zf1_11/public_html"
    ServerName zf11.localhost
    <Directory "C:/wamp/www/zf1_11/public_html">
        AllowOverride All
        Order allow,deny
        Allow from all
    </Directory>
</VirtualHost>