ISP Trace

http://visualroute.com

BTW reporting them isnt likely to help anything because they could be using a proxy, spoofed IP, have multiple people on the same IP etc.

If you just have their IP and not email address, it sounds to me like your firewall reported they "pinged" you. If this is the case, dont bother reporting it, bc the ping did not get through, and without Pinging the internet would not work, it is totally harmless to be pinged.

VisualRoute is for location, but you can use
Tracert for all the network hops, and usually find the ISP, or use any WHOIS to look up the IP and it willl find which ISP owns that IP.

You can look up an IP address at:

http://www.arin.net/whois/index.html

But you cannot personally identify the person that way. It will tell you who their ISP is though.

Not necesarilly who the persons ISP is, its extremely easy to spoof an IP or use a public proxy.

That's true. Sometimes it will tell you the ISP but not all the time. I stand corrected.