Networking: setup help needed

[Cavelion]

Hello all,
I hope somebody can explain how I can go about on getting the following needs configured.

For testing purposes I want to following set up.
7 Virtual Machines consisting of:
1 Clarkconnect server operating in stand-alone mode (so one network card only, no need for DNS, DHCP, ...)
4 Windows XP machines (one network card per VM)
2 Vista machines (one network card per VM)

Each computer should work in a NAT mode, however all the VMs should be on the same Virtual Lan. So all my Host PC does is routing internet traffic.
So in essence I need a NAT network.
Bridged networking is not an option, because the computers may not communicate in any way with my host. (My host is "as if" part of the internet)
Internal networking doesn't cut it either, because if I understood the manual, only communication happens between the VMs. But then I miss communication to the outside world, and my VMs need to be able to access the internet.
It is not an option to put the Clarkconnect server in bridged mode (with a second card) as I want to replicate a real network situation where this is not going to happen. (Router + Switches + Clarkconnect Server (Planned) and many XP and Vista machines).

Can someone please explain if this is possible? And if yes, how to configure VirtualBox for this setup.
Probably I need to fiddle with the NAT settings but I haven't figured out yet how.

In a future case study I will even need two of such network configurations to try to work out how to do VPN communication between those networks and testing out NetControl 2.
Would it be easy to configure this with portforwarding or would it be wise to add an extra VM per network which implements a Router (PC, do only DHCP, DNS and VPN services) like an extra Bridged Clarkconnect Server (dual LAN: bridged and internal networking). Or can anyone recommend an easier way (free OS and easy to configure) to implement the functionality of a router present in the system.
If the later route is the easiest I think I better go with the extra VM.

Thanks,
Cavelion

[vbox4me2]

It is pretty basic, you're going to need NAT for all VM's, you can't dedicate 8 NIC's to 8 VM's, they all use the same master Host NIC. I would advice to use Bridge mode anyway and use a private LAN range outside the rest via a VM acting as a router, it will seperate everything while keeping options open to access VM's in any direction.

[Cavelion]

Well I have indeed decided to go ahead with the extra VM: a clarkconnect server merely simulating a basic router. DNS, DHCP, and IPSec. This VM have a bridged and an internal networking interface.

It will be easier in the long run.

Thanks for helping me make that decision a bit easier vbox4me2.

Cavelion