Why do you need the IP address?
The NC should scan for a wifi connection. Once you identify your wifi choose it, enter the passkey and the NC should connect.
I'm assuming you meant MAC address (for a MAC whitelist). If this is the case, obviously the simplest option is to just turn off MAC filtering on your router, and then re-enable once you get the MAC.
On the other hand, if what you're trying to do is assign the Nook Color a static IP, then unfortunately you'd be out of luck. There's no way to assign a static IP on a (non-rooted) Nook Color, so you'll have to allocate at least a small range of IPs for DHCP on your router. If you're willing to root, then you can use an app like Wifi Static to get around this issue.