If all you want to do is learn your Cisco skills on an 800 series, you don't need to do any configuration on the 2Wire.

Just run an Ethernet cable from the 2Wire to your office, like oyu described.  Plug that cable into any Ethernet interface on the Cisco 800.  Then run another Ethernet from a different interface on the Cisco to your computer.  Then you'll need to configure the Cisco to route and use the following features:

- IP routing

- NAT

- DHCP on the 2Wire side

I have an example Cisco configuration earlier in this thread.  Look at the interface that's labeled as the internet interface and see how it's configured for DHCP.  Once you get the Cisco configured properly, it will route with NAT and your wired computer will be able to access the Internet.

This will also allow the 2Wire to continue routing and using wireless that will be unaffected by your configuration changes on the Cisco.