If you want the two machines to communicate with each other, you don't want to use NAT, since your machines will basically be behind a firewall. You want to use bridged network adapters. This document provides a great overview on the differences between the different networking modes.
If you're using bridged network adapters, the host systems should be able to communicate not just with each other, but the rest of the world. Some things I would try:
- Not responding to pings can be totally normal. Are the systems configured to respond to ICMP requests?
- Can both systems ping google?
- Does your router show the DHCP leases?
Hope this helps.