Hmmmm...
While I know alot about IP routing, I unfortunately know little about XP. Try this:
Go to control panel / network and choose the wireless adapter.
Open up the properties for IP and click on advanced. Choose 'gateways' and if there's an entry for 0.0.0.0 change the metric to 2.
If there are no gateways listed, you can try adding one.
You can use 192.168.1.2 as the gateway, just set the metric up to 2, that way even though you have 2 default routes,windows should use the one with the lesser metric.
If you're using DHCP things might look a little different...
If you get stuck, feel free to email me directly....
rapple-at-ciscodotcom