3Com WL-542 - Manual (Page 69)

Firewall 67
To put a computer in the DMZ, enter the last digits of its LAN IP address in
the Static IP field. Put the IP address (if known) that will be accessing the
DMZ PC into the Public IP field, so that only the computer on the Internet
at this address can access this PC without firewall protection. If the IP
address is not known, or if more than one PC on the Internet will need to
access this PC, then set the Public IP to 0.0.0.0.
Click Apply.