First thing in any such situation it to do a factory reset on the router! Most are designed to work out of the box (for this very reason). Of course, then you'll want to add in wireless security, an administrative password, etc.
Of course, all of this assumes there is internet access available via that ethernet port on the wall. So this is confirmed? Can she connect here computer to it directly and have it work?
One other possibility (as assuming the above is not an issue). It's *possible* the landlord is using MAC filtering to limit access to known, approved devices, like her MacBook. If so, she'd need to either have the landlord add her router's MAC address, OR, clone her MacBook's MAC address to the router's WAN.
I entered the Subnet Mask and Router (with a 2 instead of 1) in the DGL-4300 router settings.
I turned DHCP off. IOW, I turned this router into a switch/access point.
I connected the wall to a LAN port (because I assumed there was already a router "somewhere").
I connected the Macbook to another LAN port.
The internet works in this setup. However, wireless does not get to the internet, either for the Macbook, or an iPod. I know the wireless connection works because both the Macbook and the iPod can access the router page. It's just that the internet only works "wired" from the Macbook. Does this have anything to do with "MAC filtering"?
Here's another possibility. It may be that the upstream router is using the same network as the DGL-4300. If so, that's an invalid configuration and you need to change the DGL-4300 to something else (e.g., if the upstream router is using 192.168.1.x, perhaps make the DGL-4300 192.168.2.x). Otherwise, if they're the same, routing is ambiguous.
You can check to see if this is the case by comparing the network the computer uses when connected directly and comparing it to the one the DGL-4300 uses by default.
And yes, as I said previously, it could be MAC filtering too, although I think the above is much more likely. It's a common error because the 192.168.1.x network is itself so common, and so both systems have a very good likelihood of using the same one, again, that would be an error in configuration.
Well that's interesting. That appears to be a legitimate public IP address, not some upstream local router managed by the landlord (which is what I had assumed). So the default 192.168.1.x network of the DGL-4300 should work fine.
As I said before, I would try cloning her MacBook's MAC address to the WAN of the DGL-4300 router. That would get around any MAC filtering that may be going on. We know the MacBook MAC works, so cloning it fools the ISP into believing it's the MacBook again, when in fact it's now the router.