The default speed of the Start Menu is pretty slow, but you can fix that by editing a Registry Key. Fire up the Registry Editor and navigate to the following key:
HKEY_CURRENT_USER \ Control Panel \ Desktop \ MenuShowDelay
By default, the value is 400 (actually the number is timeout in milliseconds). Change this to a smaller value, such as 0, to speed it up. You may not have this registry parameter at all. In this case, you need to add it. On the Edit menu, click Add Value, and then add the following registry value: "MenuShowDelay"=0.
You may notice that setting the registry value to “0″ might be too quick for your mouse to respond. If that is the case, put the number higher, say 100, and check the effect on startup.
If this doesn't work for some reason, then you might try the following: Navigate to Display Properties then Appearance then Effects and turn off the option titled Show menu shadow. You will get much better overall performance.
Caution: Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on your computer.