Linux - VirtualBox and connecting my linux server

Hi folks,

I am an amazed new Mac-User and installed VirtualBox 2.1.2 on my Macbook Pro. I configured host networking with connection to the Airport device en1. While I am connected to my wireless network at home I am able to connect to the guest system (Linux Server) from my Mac host. If I was off-line and so the airport device is not connected, the guest server gets its static ip but I can not reach the guest through my host.
Is there any network issue and solution? I want to test my LAMP server even without a established real network connection. I think there must by a way to configure the airport with static ip if there is no dhcp available.

Any hints and help appreciated.

Bye,

Holger