How do you set up a D-link 4100 and a Vonage properly?

My network goes Modem > D-link 4100 > Vonage router.

Ever since I replaced my old router with the D-link I have been getting lag spikes in multiplayer games. What I did was take my lan wire and plugged it into the Vonage instead and the lag spikes went away. Why is it when I do this instead of plugging directly into my D-link I get no lag spikes. The D-link is a gaming router and wouldn't you have the best connection plugged directly to the d-link? Is there a setting I need to change in the Voange router so I can benefit from Game Fuel or do I still get game fuel if im plugged into the Vonage router?

There are 4 computers in our house so only 3 can be plugged into the d-link so 1 port is free to hook up to the Vonage router.