If you use Gaim messenger, then check this out :

Open

C:\Documents and Settings\’user’\Application Data\.gaim

or

C:\Documents and Settings\Administrator\Application Data\.gaim (in most of the cases)

There are two files named prefs.xml & accounts.xml

Right click the accounts.xml file and open it with notepad or any other text editor. Here you will easily find your usernames & passwords in simple text. So, never share these two files with anyone.