Since I, who have a decent working knowledge of networking, had a somewhat hard time following OP's instructions I'm going to put together a step-by-step for the uninitiated. I'm afraid my advice with router settings may not be helpful if you don't have the same one I do (Linksys WRT54G) but you'll be able to find what you need online.

1. Logging into your router
1.1 Enter router IP into your web browser.
1.1.1 Router IP varies with the router. Mine is 192.168.1.1, but others will be 192.168.1.0 or 192.168.0.1. If you aren't sure simply google the make/model of your router and you should find a a manual that knows it.
1.1.2 Your router will request a password. By default this is usually "admin"/"admin", ""/"admin", or "admin"/"". You can google your make/model to find out what the default is.
1.1.2.1 If you changed it and don't remember what it is your router will have a reset button which, when pushed, will reset all settings, including login/pass, to factory defaults.
1.2 Find your DHCP settings
1.2.1 For my router this is on the initial page (basic setup).
1.3 It will have a range or starting point for IP addresses. Mine is a starting point of 192.168.1.100. Take note of this value and make sure whatever this range is does not include all possible addresses. By having a starting point of 100 My DHCP range is 100-255, for example. Set your range so that at least one value other than the router's IP cannot be assigned by DHCP.

2. Setting up a static IP for your PS3
2.1 In your PS3 main menu find settings->network settings->internet connection settings
2.1.1 Custom setting method
2.1.2 Continue as appropriate until you get to IP Address Settings
2.1.2.1 Select Manual
2.1.2.2 Set the IP address to something outside of the DHCP range you set in 1.3.
2.1.2.3 Set the default router to the router IP address. This is the same thing you put in your web browser in 1.1.
2.1.2.4 Set the Primary DNS to the router IP address.
2.1.3 Handle MTU and Proxy server settings however you normally would.
2.1.4 Set UPnP to disabled
2.1.5 Save and test connection.

3. Changing router settings
3.1 Disable UPnP in your router
3.1.1 For me this is under the "administration" tab.
3.2 Set DMZ to the IP you selected in 2.1.2.2
3.2.1 DMZ will be found under "port forwarding" or "applications". Something like that. My router calls it "Applications & Gaming".

Hope this helps. Let me know if I forgot something.