How do I find the IP address of a network attached device?

[Law]

This was late, but tracer route will not work for this situation. The access point is nothing but a hub, packets are going through the default gateway, that's the only route your computers knows how to get to another network.

Ethereal will be your best bet for listening on arp broadcast while the laptop trys to connect to the access point you run it on a computer wired to the router.

EDIT
Or try this, connect a computer directly to the access point with a wire and use Ethereal, see what it reveals.

 

[technogab]

Do an IP scan

Try using the free utility AngryIP scan. It works great for scanning IPs on your network and even resolves host names

http://www.angryziber.com/ipscan/