You need to configure your Belkin router as an access point, and setup a bridge between the networks. It varies from router to router for the setup - do you have the exact make/model of the router? (Both the Belkin and DSL Wireless Gateway).
Yes I do; The Belkin number is F5D7230-4, VER A000 and the DSL gateway is Cisco DPC3825. The Belkin control page has an option to make it an access point; is that what I want? And if so how exactly do I configure it?