If the Guest OS Firewall and Web Server are properly configured then you should be able to access it from the Host using the Guest OSes IP Address however you cannot use localhost from the Host to see the Web Server on the Guest OS as localhost is just that, meaning local to the host itself and nothing beyond the host itself and each system, physical or virtual, has its own localhost and this is by default a loopback to itself. So unless you, what I'd call IMPO, wrongly modified the hosts file to allow the loopback adapter to point to a location outside of the host itself then you cannot and should not be able to use localhost in a browser on one system, physical or virtual, and access a Web Server on a different system, physical or virtual! 
While that certainly can be done nonetheless it shouldn't be and it breaks the expected defaults although I have see some users do it anyway.
You need to use the proper IP Address, in this case if the Guest OS is hosting the Web Server then the IP Address of the Guest and if applicable the Port Number if other then 80 and cannot use the Domain Name unless it's registered in the DNS or hosts file.
So the bottom line is make sure that the Firewalls on both the Host and Guest are not blocking communications on the IP Address and Port(s) used by the Web Server and you should then be able to connect to it. That is assuming the Web Server is properly configured as well.
Message was edited by: WoodyZ - Originally posted, Feb 18, 2013 12:48 PM.