to do a reverse lookup and find the DNS name of the IP
ping -a 192.168.0.1
where 192.168.0.1 is the IP.
perform a traceroute :
tracert 192.168.0.1
where 192.168.0.1 is the IP.
Some of this may give you a clue as to the ISP of the user. If you are serious about taking some action, call the ISP and complain. If they are using static IPs, they will know right away who did this. If not, they will probably be able to look up which user account was assigned that IP at that time. So you need to know the time that this happened. They may be able to warn or ban the user. That's the best you can do, but even pulling this off may be difficult.