Yahoo Messenger & Gtalk could be enabled for multi user logging. It will be helpful if you have two IDs or you & your sister/brother wants to be online.
To enable multiple login in Yahoo messenger, you need to add a registry entry. Instead of doing that manually, you can just download registry file here. Double click that registry file & restart Yahoo Messenger. To disable this option, download registry file from here & double click it.
Trick by Daydream
1. Create a shortcut of Google Talk messenger on your desktop or any other preferred location .(To create a shortcut, right click on your Google Talk messenger application and select Send To–>Desktop(create shortcut) )
2. Right click on the Google Talk messenger icon and select Properties option
3. Modify target location text “c:\program files\google\google talk\googletalk.exe” /startmenu to
“c:\program files\google\google talk\googletalk.exe” /nomutex
Trick by Tech Dreams