If you don't like the Blog I published yesterday (Using Large Icons in the Taskbar's Quick Launch Toolbar), because the size of the icons are enough already and using large icons makes your desktop looks bulky.
Use the Keyboard Shortcut instead!
Windows Vista automatically assigns keyboard shortcuts to icons on your Quick Launch Toolbar. Just use the Win key + position of the icon.
Example: Win + "1", for Internet Explorer and Win + "2", for Firefox