->start\run\regedit32
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Current Version\Run
HKEY_CURRENT_USER\Software\Microsoft\Windows\Current Version\Run
There you should find the lines that launch the bar at startup (among other sometimes usefull things). Edit the line that launches the search bar (you'll have to guess the right one) and add "rem" without the quotes at the beginning. Restart the computer, and make sure that the bar isn't loaded anymore. Check the folder where the registry entry pointed to. Search your hard disk for copies of the files you find there (these pests tend to install themselves at multiple places), and delete anyting you find that matches the files names.