Not really sure that I understand what you are saying.
Assuming that you are trying to configure an outbound VPN connection on each of the machines, and you lose connectivity otherwise on each machine as you start the connection, try:
A) Uncheck the 'Use default gateway on remote network' box -- connection properties --> Networking tab --> click on TCP/IP, then Properties --> Advanced
B) Check your addressing scheme. The network address of the local network can't be the same as the remote network -- for example, you can't use 192.168.1.xxx on both sides with a netmask of 255.255.255.0
If I haven't hit your problem, you're going to need to provide more details.