You can delete this entry from the registry:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
RESTART_STICKY_NOTES
Or, try to delete this file C:\Windows\system32\StikyNot.exe (make a backup first).
Another option would be to disable the sidebar (Windows Gadget Platform). See a tutorial here: http://www.howtogeek.com/howto/3255/disable-sidebar-desktop-gadgets-on-windows-7/