DGL 4100 Router Cannot Connect To Internet Via WAN Port?

I'm trying to change the way my network is set up by replacing an old cheap Switch with a newer Router that has some QoS options.

Modem: Motorola SBG900 LINK (provided by Time Warner, not purchased by me)
Old Switch: Zonet ZFS3008 LINK
New DLink Router: D-Link DGL-4100 LINK

Currently, my network is set up as follows, arrows being Ethernet cables:
Cable Modem w/ Wireless <-------> Old Switch <-------> 3 PCs and a Printer

With everything set up as shown above everything works fine, but I want to change it to:
Cable Modem w/ Wireless <-------> DLink Router via it's WAN port <-------> 3 PCs and a Printer

Simple change, right? Apparently not.A few things aren't working when I swap the DLink Router for the old Switch.

1. Internet does not work, though I can log into the DLink Router in a web browser and see all of the settings.

2. The IP address that used to go to the Modem (192.168.0.1) now goes to the DLink Router, and I cannot get to the Modem anymore via a web browser with any IP address.

3. The wireless from the Modem stops working.

4. I see the following when logged into the DLink Router and looking at the Status tab:

. . Connection Type :DHCP Client
. . Cable Status :Connected
. . Network Status : Establishing (Please Wait...) (it never establishes)

I have noticed that the DLink Router and Cable Modem both are doing DHCP, and I am wondering if that is creating a conflict that is causing the problem. However, simply disabling DHCP for the DLink Router and otherwise leaving the connections as they are still does not get the internet working.

<----------------insert a couple hours of fiddling with it some more------------->

The following setup works as far as letting everyone online, but QoS rules in Gamefuel are not getting enforced:

Cable Modem w/ Wireless (DHCP enabled) <-------> Old Switch <-------> DLink Router (DHCP disabled) via LAN port, leaving WAN port unused <-------> 3 PCs

I can now log into the Cable Modem via 192.168.0.1 and the DLink Router via 192.168.0.2. The wireless internet is also working again as well. My PC uses Windows 7, the other two PCs we have are on Windows XP and Vista.