Talktalk and belkin wireless, help please?

Hi i read this: http://www.wirelessforums.org/alt-in...html#post70249

But i cannot set MTU to what was suggested as it is too high apparently?

And i don't understand what the person meant by "Oh,one more thing.The supplied filter must be connected close to the
back of the router,
not plugged directly into your telephone wall socket as this stops the
signal reaching the router."

You can't connect the phone filter to a router, the connection on the end is too big?