1) Open Command Prompt. Have some one on yahoo messenger send you a file; while the file is sending, in command prompt type -> netstat -an press enter
2)it will show alll Active Connections on your computer, in there under foreign ip for a number thats ends in 5050. this is the persons ip adress who is sending you the file
3)Now type : net use: h \\ (the person's ip adress)\shareddocs push enter wait for message to show up
4)If it is successful you should get a message saying command prompt was successful. If you get a error message than your attempt has failed, probably because the person has security measures in place to prevent hacking.
5)if you get the message that says command was successful, than go to my computer. There you will see a file named "shareddocs on (the name of your computer)" open this file
you are now connected to that person's computer.