The default host-only networking in Server 2.0 and Workstation allows the guests to talk to each other and also to the host itself. What you may want or need to do is to have host-only networking where the guests can talk to teach other but not to the host and vice versa. This is actually very easy to setup. I would suggest that you create a new host-only network adapter for this so that you can also have "traditional" host-only networking available too.
For Windows hosts (I tested this with Workstation 6.5.1 running on Vista SP1 x86), it is simply a case of disabling the VMware NIC on the host.
For Linux hosts (I tested this with Server 2.0 build 122956 on openSUSE 10.3 x64) , I found that if you just take the network interface down (e.g. "ifconfig vmnet3 down"), although the guests cannot ping the host's IP address, the host can ping its own ip address. I therefore also removed the IP address from the interface on the host. This is achieved thus (obviously substituting the correct IP address, subnet mask length and network interface):
ip address del 192.168.188.1/24 dev vmnet3
I've not exhaustively tested this, just used WinPE bootable ISOs and pinging another host-only VM and checked that they cannot ping the host's host-only IP address. Note that the guests still get IP addresses via DHCP (if configured that way). There may also still be some communication possible between host and guest but simple IP based stuff seems to be disabled.
Given the similarity between Workstation and Server 2.0 at the network level, I would assume that each of the methods above will work on both Windows and Linux.
