When you are adding a line to the host file like this localhost mywebsite
And by telling the httpd-vhosts.conf file what line you added to the host file what is going on ?

Have you set the include path in the php,ini to point to the right place(s)? The section in the php.ini will look like:

; Paths and Directories ;

; UNIX: "/path1:/path2"
;include_path = ".:/php/includes"
; Windows: "\path1;\path2"
include_path = ".;c:\php\includes;c:\php\example"

Add one for each web app, separating them with a ;
Do you have to worry about this and what does this relate to with client request ?