I just downloaded and installed the new GNS3 VritualBox version. So I immediately built a simple topology with a small router, an Ubuntu 11.10 server VBox image connected through a virtual switch.
The issue is that I can't get them working together. I used the simplest option in VirtualBox i.e. i left the network adapter to NAT (see the attached screenshot).
Now, when I start my virtual machine in GNS3 I get the following network configuration automatically:
"intet addr: 10.0.2.15 Bcast: 10.2.0.255 Mask: 255.255.255.0"
I also get a default route on the virtual machine pointing to 10.0.2.2. All this without any configuration from my side. I guess it's the default.
On the router I should configure my Fa0/0 interface connected to the virtual GNS3 switch manually. But this is the part that I miss:
1. How is the connection to the VBox image from GNS3 achieved? If there's a NAT working as an "abstraction layer", or more or less like a virtual NAT router, than can't ever get direct IP access from the simulated router.
2. How should I configure my router in order to access the VBox image? If there's a virtual NAT router, how can I configure than my router in GNS3 to access the network behind it?

I also tried all other different options for the network adapter in VirtualBox but none of them seems to work. For example the Host-only Adapter option gives me an address from the 192.168.56.0/24 network with a default gateway pointing to 192.168.56.1. Which is cool, but again, how to network with another emulated device?
I also noticed that each time I connect and start a VBox image in GNS3 a second adapter appear in the VirtualBox configuration for that machine, it's visible in the screen shot.
So the question here is, am I missing something?

I forgot. Here's also an output from the dynagen console:
=> show run
autostart = False
[127.0.0.1:7200]
workingdir = D:\GNS3_temp
udp = 10000
[[2691]]
image = D:\Install\dynamips\2600\C2691-adventerprisek9-mz.124-25d.BIN.uncompressed
ram = 128
idlepc = 0x60a48e60
ghostios = True
[[ETHSW SW1]]
1 = access 1 VBOX1 e0
2 = access 1 R1 f0/0
[[ROUTER R1]]
model = 2691
console = 2000
f0/0 = SW1 2
[vbox 127.0.0.1:11525]
workingdir = C:\DOCUME~1\bg100039\LOCALS~1\Temp
udp = 20900
[[VBoxDevice]]
image = UbuntuServer_11.10_32bit
nics = 1
[[VBOX VBOX1]]
e0 = SW1 1

OK guys. I finally did it!
I used the "NAT" option for the interface. And when I add my VirtualBox VM in GNS3 and connect it to another networking device additional interface appears in the VM. So I just disabled the main interface and added my IP configuration there. And it works...
So how can I mark this thread as solved now?