I have a D-Link N300 and I want to connect it to another wireless router, so I may provide Internet access to my wired network in another room. Is this possible?
As long as you disable the dhcp server on the N300 it should be OK.
If you're looking for expanding the wifi signal I sugest you read how to configure WDS (http://pt.wikipedia.org/wiki/Wireless_Distribution_System ) on both devices (usually just activate and enter the macaddress of one on the other).
If you wanna connect them by cable just connect a Rj45 UTP cable on one of a LAN port each device and it should be OK