Issues with DHCP and NAT and Time Capsule and Xbox 360

Hey y'all. I've been having very frustrating issues with my Time Capsule. I've tried nearly every suggestion on the internet. Few of the solutions involve Leopard and even fewer the new Dashboard (which is fine since the settings are pretty much the same). It seems that NAT is causing issues. I can connect to Xbox Live to, say, update the console and download demos. But I cannot get past NAT. I'll get a screen that says NAT is too strict. When I go in Airport Utility to setup NAT and DHCP I can't get past an ending DHCP address. Now I don't know ANYTHING about Networking. I'm great with Macs in general, but networking is out of my league. How can I get an ending DHCP address? I try everything from 192.168.1.000-192.168.1.90 and nothing works. Can anybody help?