How do I force XP to use a certain wireless network?

There are two networks, default and NETGEAR. I want it to connect to 'default'

Well, you'd have to add default to the list of preferred networks in the Wireless Networks tab of the Wireless connection - assuming you are using XP to manage the connection. Look in your Network Connections control panel for this.

Then in the Advanced button, make sure "Automatically connect to non-preferred networks" is UNCHECKED.

That's it.