In Windows XP, by default there is a delay in displaying the Start Menu when you click the Start Menu. This is a delay induced by purpose to allow Mouse Response times. However, the default delay time might just prove a bit too long and make you feel Windows is slow.
To speed up the Windows Start Menu, edit the value of the Registry Key and set a lower valus which suits your need. Beware, setting it to “0″ will be too quick for your mouse to respond.