You need to setup a virtual host in apache, this is from my web config.
Code:
<VirtualHost *>
ServerName pics.w00ttech.com
DocumentRoot /www/w00ttech/webroot/pics
</VirtualHost>
<VirtualHost *>
ServerName mail.w00ttech.com
DocumentRoot /www/w00ttech/squirrelmail
</VirtualHost>
If you want to be able to access the apps from
www.app1.com or
www.app2.com you are going to have to either own those domains or setup a dns server on your localnetwork that will resolve the address to the correct IP.