try plugging your pc into the yellow port, only plug the pc into the spa2102, no internet port, no wireless on the pc. your pc should get an IP address on the 192.168.0.x network
go in your browser to http://192.168.0.1
click admin then
click advanced
go into the gui,
router tab --> lan setup --> lan ip address specify an address range that's not on the same network as the other router.
go into router tab --> Wan setup and enable the wan web server (this will allow you to get to the ATA from your main network.
then plug the "internet" port into your lan note the dhcp address on the status tab, or set a static.
enter the proxy, username and password in line 1 and you should be registered
look under voice --> status to see registration status or see if you have dial tone.
Dan