Most of the time, when people say they have a networking issue, I suggest updating the firmware. This time I suggest downgrading.
Since installing a DG834G at home my online gaming has been abysmal. I spent some time playing about with port forwarding/upnp etc but no luck. A quick search online showed a few forum entries where people mentioned the firmware I was using (the latest) seemed to be the cause. I downgraded from version 5.01.14 to 5.01.09 - immediate improvement.
Strange but true.