Need help with Comp-to-Xbox Networking!

[Needz_Help]

I have a Dell Computer with Verizon DSL. My Westell modem is connected to my comp through USB type "B". My modem is connected to my D-Link DI-524 through Ethernet. My Xbox is then connected wirelessly to my router by the Logitech Xbox rwireless adapter. My problem is that I can't have both my Xbox and Comp connected at the same time. Why is this? When my comp is connected, my Xbox says that the DNS was not resolved. Is there any way to fix this? I am not very computer litterate, any and all help will be greatly appreciated!