(OK)(OK) using adb with a NAT'ed VM - VirtualBox - NAT Port Forwarding

http://www.android-x86.org/documents/debug-howto

The steps above work nicely if you have a VM which is set up to use Bridged or Host-Only adapters

However, if you have a NAT'ed VM you cannot connect to the VM IP from the host

You will need to set up port forwarding for a host port to be forwarded to the VM port 5555 (which is adb)
VBoxManage modifyvm <VMName> --natpf1 adb,tcp,*,<localport>,*,5555
Example from one machine:
VBoxManage modifyvm froyo --natpf1 adb,tcp,*,5555,*,5555

Once this is done, you should see the local port (i.e. 5555 in this case) bound on the host via netstat -a

You can now connect to the VM by adb localhost:5555