How do I connect 2 Xbox 360 to a Motorola Netopia?

[boo]

Me and my friend are trying to connect 2 Xbox 360's to my Motorola Netopia (don't really know if anybody needs to know what type), but everytime we are able to both get on, we can't be in the same party, nor play the same games...expect for Netflix. Right now, I connect both him and I to another router of my, a Linksys, and again we were able to connect but yet again we can't do anything together. I called my IPS and the guy told me I will probably have to get another IP, but he really didn't go into detail with that. If I have to get another IP, then could someone also explain how to get a second one. Thanks