Have just purchased a B683 router from 8ta but am battling to set it up for on-line gaming on a PS3?

It seems my NAT setting is an issue (not sure what this is?), keep getting an error msg that I've got a moderate to strict NAT settings which do not allow me to set up a multiplayer game in Black Ops? Have searched on the net and found something on how to open NAT on the PS3 side using a static IP address and then allowing that address on your router, however not sure on how to configure this on the B683? Am a total newbie with this so pls be as basic as possible? Also I've tested using both 8ta and MTN sims but keeps getting the msg that "IP fragments are not supported" when using the 8ta one?