How to get rid of an unknown IP/mac address on my netgear wgr614 router?

I have an imac (ethernet connection), mac book, PS3 and iphone hooked up to my router and have been having ALOT of trouble with my ps3 lagging while playing COD4 so i have been messing around with the router settings and checking the attached devices b/c I am trying to set up static ip address with my 2 macs with no luck, when i type the address in the macbook network settings the signal is good but no internet. I have successfully set up my PS3 with a static IP and forwarded it to a port, but still it lags!!! btw i have comcast cable, resetting the modem and router only smoothes play for an hour or so - if at all.

Now to the new problem thats made me do back flips in my apt for the past few days. There is a 5th device connected to my router, with an ip and mac address. I have changed my ssn (which is now hidden) and pw 2x and my router login pw. Just to clarify so im not getting worked up over nothing, if all my devices(4) are connected to my router and there are 5 devices attached (ip/mac addresses) does this mean someone is hacking my internet/computers? If so what do i do? Also is anyone else having trouble with lagging issues on cod4 with comcast cable and vonage phone service?How to get rid of an unknown IP/mac address on my netgear wgr614 router?
er well first thing is that you need an Static IP from your ISP



Then you are then best to set up addresses as DHCP from the router



and if possible use ethernet cables instead of wireless



Your question is a bit complex to answer in one, try connecting you XBOX on its own and see if the problem exists, if not then by a process of elimination find out which bit makes it go ';Wrong'; jst pointers really but hope it helps