Atheros card as LAN?

[srynoname]

I got a new box with two network adapters:
1 x wifi ath0 (atheros wlan card)
1 x ethernet em0 (onboard lan)

I want to use the atheros WLAN card as LAN. What's the best way to do this? Especially how to configure it without having access to the LAN interface (and therefore no access to the webinterface), as yet no WLAN is set up?