Why won't my Xbox wireless adapter connect properly?

So I just upgraded my wireless adapter to the relatively new wireless-N model and gave my G to my girlfriend. But now whenever I turn my xbox on and try to log into Live, it won’t work and tells me the xbox can’t obtain an IP address from the router or modem. I have to go manually reset the router and modem each time. Thing is, my computer and phone are both logged onto the network with no problems without having to reset. What’s up with that?
On a separate note, when it is connected (after the manual reset) it says its only connect to wireless-G though I have a wireless-N router. Any thoughts to what’s going on here?