It's less of a matter of where, but as what. IP log should be under xf_ip but they aren't stored as readable IP addresses. There is a post somewhere but I am pretty sure anyone who has ever written related plugin can explain it as well. I believe the date to which IP's are kept is adjustable but the shared tool is probably hardcoded.
Never seen or looked for the hostnames. Perhaps its a live lookup? I know at least with the plugins I have installed the hostnames are recorded on registration and in the spam trigger log, but as far as if any of that is stock... eeek lol.