My C&H inspired siggy is far better. :)
BACK ON TOPIC: If you are mearly going to sniff their IP to turn them in, don't bother. If you wanna sniff thier IP to hack them back out, I'd suggest you first find out if they are connecting to your comp directly, or mearly hacking the server to get ur bro's acc info. If it's the former, you aren't getting their IP. IF it's the latter... you'd be able to get it real easy by just seeing what IPs you are connected to. (That's the cmd prompt thing some1 else mentioned... but only works if they are directly connected to your comp.)