I have 2 virtual hosts running on my Windows XP laptop. One is Ubuntu running inside vmware player. The other is MS virtual PC (so I can test with IE6 ). The Ubuntu virtual host is running my web application with apache. I can point my browser on my laptop at the Ubuntu IP and view my web app. I read this post How to connect to host machine from within Virtual PC image and was able to get my Virtual PC to ping my physical machine using the loopback adapter. But I'm stuck on getting my Virtual PC to see my web application running in the Ubuntu vmware player host.
I think the best is to configure both Virtual machine with "Bridged network interface" so that they all get an IP Address from the same DHCP (the same as your host machine) and they will be in the same network.
Otherwise the only common thing between two NAT is the host machine. Perhaps configuring a special routing from one subnet (vmware NAT) to the other (VPC NAT) can work, but honestly I never tried it.
I would prefer my first solution, with a firewall enabled on both VM (and configure exceptions one by one).