Methinks you should read up on what you are trying to do!
Now I'm not sure exactly how ISPconfig does things, but a standard Apache2 install comes with the home directory pointing at /var/www however it looks like your server already has virtual hosts enabled. Virtual hosts allow you to host multiple sites on one server and point folders in any directory to the internet.
Now it looks like you could possibly use just mod_rewrite and a basic install of Apache2 to accomplish what you want, but you already have virtual hosts configured so I say use them!
Here is a great tutorial that should get you up to speed in no time. Be patient! Apache2 can be frustrating but it seems like every day I learn something new about it!
http://httpd.apache.org/docs/2.2/vhosts/examples.html