Ok, long story...
I have two VM's running in Virtual Box. Both are configured with an internal network adapter and a NAT'ed connection (for internet connection only). One VM is running CentOS 5 and the other is Win2k8R2. I setup the internal network with hard coded IP's in the Class C 192.168.xx.xx subnet. I am also running DNS from my host OS. Both VM's can resolve each other's IP's and the Windows box can ping the CentOS box. However, the CentOS box cannot ping the Windows VM. I disabled the Windows firewall so I am pretty sure the its not getting blocked.
At one point I was using VB's DHCP server for the internal network and the CentOS box would get an IP, so eth0 is able to talk, and ping to other external systems work fine.
For the internal network both machines are not using a default gateway since they are both on the same subnet.
Anyone else have any ideas?