Hyper V Routing Issues

I have setup my virtual network using Microsoft Hyper V in Windows 2008. My virtual network sits in the 172.16.x.x subnet within a private virtual lan - I have set the network cards for these virtual servers as access to the private network only. I have added one virtual machine with two network cards rinning windows server 2003 with RRAS - one virtual network card allocated to the private virtual network (172.16.x.x) and the other virtual network card has been mapped to my perimeter network (my perimeter network consists of my home PC's on my home lan which sit on the 192.168.x.x network).

<<perimeter network(192.168.x.x)>> --|Windows 2008 Hyper V|--<<Virtual network(172.16.x.x)>>

On my virtual RRAS server I have setup only routing capabilities between my two networks, I have confirmed that the routing table is correct and the IPEnableRouter is set to 1 in the registry. I have added the necessary routes to the machines in the perimeter network so they can forward the packets to the correct gateways.

From my virtual RRAS server I can ping both my virtual network machines and my perimeter network machines. from my pc in my perimeter network i can ping both ip addresses on my RAS server - however my issue comes when i try to ping another virtual machine which is not the RRAS server, such as my virtual DC from my PC in the perimeter network (I have added the necessary static routes for this machine).

In ethereal i can see the ping request reaching my virtual DC from my perimeter network machine, and I can see the ICMP reply being sent back but I cannot get the ping to reply for some reason, I have double checked all the settings over and over but cannot find a solution.

Is it something to do with hyper V - does anyone have any solutions??