|It will be almost impossible to find the IP address of a instant message. There are a few exceptions however. For example, if the instant message comes from a AOL Instant Message user who is currently has a "Direct Connection" to you (through the AOL IM program), you can use netstat -n to find that persons IP address.|
If you want specific help you'll need to tell us what IM program you are using, what IM program the other person is using, and all other specifics.
Finally, what do you hope to gain by finding this persons IP address? Blocking that IP is possible, but it's not hard to get around such blocks. Tracing it to a physical location is sometimes possible, but this is rarely accurate/helpful.
Free Computer Tips and more:http://RyanTAdams.com
Paid Tech Support: Black Diamond