I will be glad to post the log and configuration files for this issue, but first I wanted to confirm it is not related to TCP chimney settings and/or the Windows 2003 Scalable Networking Pack which is included in SP2. In the forum FAQ's, there is a mention that it may be ncessary to disable some of the advanced features included in Windows 2003 SP2 such as TCP Chimney Offload on a Windows host running VMWare workstation. I am running Workstation 6.02 - build 59824 on Windows 2003 Server Enterprise x64 w/ SP2. Some of the advanced features such as TCP Chimnedy Offload are turned on by default. However, I am only experiencing issues with the guests on the same VMnet network intermittently losing connectivity to each other. Could this be the same issue? The strange part is that by rebooting the host and guests without making any configuration changes resolves the problem (temporarily). I've run network captures from Wireshark on one of the machines while the problem was present, and it shows that the ARP requests are getting through to the interface on the other guest, but it just doesn't seem able to ping.

Quick summary:
Workstation 6.02 - build 59824
Host: Windows 2003 Server Enterprise x64 w/ SP2
Guests: Windows 2003 Server Enterprise x86 w/ SP1
Network configuration: One guest used three VMnets - Bridged and two private, the other uses one Host only and one private network.