Well I would see if Netgear can help you bridge this modem if it can do that. If not, it's possible that the DMZ could be used for the 4500. I see there is a WAN Setup section on the NG modems menu. There should be a DMZ option here.
If you can't get the Netgear to work or operate in bridged mode. I would investigate finding a Modem only option for DSL. DLink has one and I think Netgear does too. Just have to find one.
If you need some help, maybe we can teamviewer in and see if we can help out some.