VPN Connection

Here is a situation I have been trying to work on for a while. We use different VPN clients(such as Cisco 3000, Nortel’s Extranet Access) to connect to our client’s LAN. We can connect fine to their LAN but we seem to loose connection with our LAN. WE can’t see anyone in the Network Neighboorhood, all the mapped drives are gone,and we can’t even ping any computer in our LAN. I have tried Lmhost, netbios, everything. But nothing has worked.Is there anyway, I can be connected to both ours and ourclients LAN at the same time?