Smart Menus

If you set this key it will turn on or off the Smart Menus feature of
Windows 2000.  If you do not use a menu item on the start menu for
a long time (1 week or so) Windows  will hide if for you & only  show
those used most frequently.  If you leave the menu open for a few seconds
the hidden favorites will appear. They will also appear if you click the
down arrow at the bottom of the list.

Details:
You can create a .reg file with this code below:
-----CUT-----
REGEDIT4

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
"IntelliMenus"="YES"

-----CUT-----
Change Yes to No if you want to turn this off.