You may try a solution here: http://answers.microsoft.com/en-us/windows/forum/windows_vista-performance/multiple-winlogonexe-processes-running/2fbb5d54-734e-406e-943e-60f207dd4eae
The answer describes that it may be a virus/keylogger and also provides an online scan tool from Microsoft for free. I would also recommend checking your scheduled tasks on startup, and see if you're running any programs as another user on login.