Putting your PS3 in a DMZ is very specific to your router... You need to know how to configure your router to:
1) Allocate a static IP to your PS3's MAC address - the MAC address can be found from the XMB->system settings->system information. You need the router to give the PS3 the same IP everytime, because you put IPs in a DMZ, not MAC addresses or device names.
2) Put the IP that will be given to the PS3 outside the router firewall (i.e. DMZ). This will probably involve creating a firewall "rule" or "exception".
Just google "<your_router> ps3 dmz"
