If you can access the internet from XP then that is good.
I would try to access the router from XP with web browser and
configure the router to use PPPOEc. I dont have SBC DSL, but have
Earthlink DSL, I then turn off the ISP dialer software on XP let the
router handle the PPPOE login.
Setting up SBC Global ISP with the router
You should be able to find PPPOE software for your linux, I just find
this setup easier.
After setting this up, try to ping the belkin, if you can't then it is either a problem with card config or routing. Make sure that you define the gateway to the belkin IP address. You should also be able to configure the linux box as a dhcp client and set /etc/resolv.conf have nameserver <belkin address>
Hope this helps.