I don't think you can just get someone's IP info.

just curious though, why do you need to change gamertag all the time? ;)

well im pretty sure if you monitor connections going to your computer i know that people bridge and the link halo 2 too boot and lag you out. Now if im correct your 360 should be getting the net through your computer.

That way a firewall such as Zone Alarm will be accepting/denying packets and connections

Live uses UDP port 3074 and 88 i think. So i would look for the connections on those ports. Obviously if you know your own IP you can filter that out. So if a connection is made to you while your gaming someone over live and the source is your connection on port 3074/88 i would assume the Ip making that request is theirs?

It may also be possible if your router supports it to monitor connections. On my netgear one it is if i tell it to log all connections i just scroll through the log and see what IP addresses have made connections on those ports. Use a simple port scanner to scan the ip address and see the host name. That usually will give you a rough idea what ISP they are. For example on WWE i scanned an IP dream train internet ISP. Gamer card says their from Japan? Bingo!

Using commview i find it very tedious but i know it works its been ages since i used it though so my help wouldn't be useful on that probably. But if you tell it to start capturing the traffic while playing games and filter all the info to those ports or something? That might do it, but its been about two years since i used that program so :p