Change The Start Menu Speed through Registry hack:Xp Tips

You might want to change the delay you notice when you click the Start menu. The default  speed can be adjusted with a quick Registry hack.
Go to the Registry key
HKEY_CURRENT_USER\Control Panel\Desktop\MenuShowDelay.
The default value is 400. Set it to 0 to remove the delay completely, but if you do that, it will be nearly
impossible to move the mouse fast enough not to activate ‘All Programs’ if you mouse over it while going to
your selection. Pick a number that suits you, make the change, and test it until you find a good compromise
between speed and usability