looking for some usefull plugins...

Check out OverRun and EZOff from Gajits.com. They might do what you're looking for. I use ShutDown Plus from TK Software, but I don't know if it can switch user (though it does support WinXP). Supposedly (according to the MS Knowledge Base), switch user and lock computer are the same thing under XP, and ShutDown Plus does support the lock computer command (look at the help file for the list of comand line parameters, and just make some shortcuts. Don't bother with the system tray program.)