In the Advanced | Special Application menu, use 47624 TCP as trigger, then 2300-2400 ports as "public ports" these are both TCP and UDP so you may need two lines to do this. And don't forget to click enabled. If you intend to play on the MSN Gaming Zone you also need to trigger on 6667 and open 28800-29100.
Some versions of the DI-704 firmware may have predefined settings for some popular applications.
Because DMZ exposes all ports it is inherently less secure. I recommend that you use DMZ only if other methods fail. You should use other means to protect the machine from compromise.
The DI-704 also has a DMZ option under Misc Items which will allow you to forward all ports to a specific computer.
D-Link recently announced a firmware upgrade that will allow the DI-804 to work with Microsoft Me and XP UPnP to allow NAT transversal. Make sure you apply Microsoft's UPnP security patch before enabling UPnP.