Please check that you have the latest driver for your Host's network card installed.
Then, can you try a test and temporarily turn off any "task offload" or other "offload" settings under the properties for your Host's network card to see if it makes a difference?
Are you running any 3rd party firewalls on your Host or Guest (BlackICE, Symantec Network Protection, etc)? What antivirus do you have installed?
This sounds like fairly standard VPN client behaviour which is to stop any incoming traffic when the VPN is up. Where is your DNS server with respect to the guest? If you need network connectivity, it "might* be possible to add another NIC to the host , use that as a manually bridged adapter, and not let the VPN client manage that link although there are no guarantees.
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This all used to work just fine and dandy under VMware Workstation_6.0.5
Since upgrading to 6.5.1, it's not behaving as it used to.
As for firewalls, we now use Symantec Endpoint Protection. It, too, is new on the system. But, as I outlined, by merely disconnecting temporarily, the guest OS can connect to VPN once it was able to ping it successfully.