Followed these instructions for putting Debian Squeeze on my plug: http://www.cyrius.com/debian/kirkwood/sheevaplug/install.html
Works great. Configured networking for one that has access to the internet for the installation. Tested ARP, PING, and tftp functionality after the install completed. Everything worked.
Modified /etc/network/interfaces and /etc/networks to point to the deployment private network. Now the plug won't respond to ARP and appears to discard responses to its own ARP requests. Verified with Wireshark that the ARP packets are valid.