Anyone knows where the contact list, messages history, and address book of Skype and yahoo Messenger is stored? I would like to know this to back it up in case I reinstall these IM's in another PC. Thanks.

Skype contact list (and perhaps message history and address book also) is saved in C:/Documents and Settings/<your account name>/Application Data/Skype. To transfer it to another computer just copy the contents of this folder and then paste it to the same location on other computer.

I cannot help you with Yahoo Messenger, i have never used it. Im sure someone else can help you with this matter.

Thanks for the info