You have to put the Xavi on bridge mode (called "monopuesto") in order for the Xavi to pass everything to the Linksys and let this do NAT and DHCP etc.
Take a look at this (scroll down): Módem Router Inalámbrico 7968r 802.11g
If your Xavi router did not come with a instalation disc to install the software assistant (Asistente de configuración) you can use the one that is on the page that I just gave you ( Asistente de configuración Amper Xavi 7968r. Versión firmware: 3.01.APT65.7968A)
Hope it helps. Good luck!--
One can only speak in tongs so many times before landing on a perfectly working spell that would turn anyone in to a frog.