Nah, any half decent linksys, for example will be able to deal with multlple connections.
For example, you could static the pc, ps3, laptop, 3ds, psp, ps3, Xperia Play, X10mini pro, ZTE Blade phones(That's a rough idea of all I have on my router)...something like 192.168.1.2, all the way up to 192.168.1.10, would allow all of them to connect with no problems, with no conflicts.
You need to have a static ip, open/forward the ports for PS3(
here!), then go to portforward, pick your router, pick the game, in this case Call of Duty: Modern Warfare 3, and follow the easy instructions, or get someone who knows their way around a router.
Is your wireless box the model TG585n, by any chance, cause if it is , it's a Thomson TG585n.
This is what you have to do, for the 02 version..there are a couple of others, just look for the Thomson, and the TG585n, version7 or 8 links on the portforward router list page, if it's different from yours
(That is, if your's is that router., which is a 3, but says 2 on it)
http://portforward.com/english/route..._Warfare_3.htm