How to Obtain the IP Address of Someone in Yahoo Messenger
Discovering the origin of the person you are chatting with over Yahoo! Instant Messenger begins with finding their IP address. While Yahoo! Instant Messenger does not have a built-in IP trace function, you can use your system's command utility as a tracing tool. Trace someone's Yahoo! Instant Messenger IP with just a few steps.
Click "Start" and then "Run" on your Windows system to open a command window.
Type "cmd" in the "Open" field. You will be presented with a text-based command line window.
Click "Actions" and "Send File" while chatting in Yahoo! Instant Messenger. Browse to a file that is at least 3MB in size and send it to your chat partner.
Return to your command window and type "netstat -n" at the command prompt.
Take note of the output from the "netstat -n" command. The last IP address in the "Foreign Address" column is your Yahoo! Instant Messenger chat partner's IP address.