That's not really helpful considering he's trying to play co-op with his brother.
King4aday, I'm having the same problem trying to play with one of my mates, his internet is fine and all other games are ok but for some reason when we try and play each other we get massive lag.
Most people say try Hamachi but I really don't want to use that, I'd rather find another solution which doesn't require a 3rd party programme.
Thanks, saw Hamachi mentioned.
Just found out my brother is playing on a flaky wireless connection, will get him wired up before checking anything else.