To install any of these plug-ins, drop the appropriate file into the //Adobe Photoshop CS4/Plug-ins folder and restart Photoshop.
The "HSL&HSB" plug-in allows conversion from RGB > HSL (Hue, Saturation and Lightness) and back, and from RGB > HSB (Hue, Saturation and Brightness) and back within Adobe Photoshop. This will allow you to make changes to the Hue, Saturation, or Luminosity of an image as independent channels, or make changes in HSL/HSB using channel operations (calculations).
Overscroll Always and Overscroll Floating (Mac only)
Overscrolling allows users to continue to pan a document even when outside of the document bounds (marked by the default grey color area surrounding the image boundaries). By default, images that fit within the document window cannot be overscrolled. To enable this behavior at all times, drop the Overscroll Always plug-in into the Plug-Ins folder and to enable this behavior for all floating windows, drop the Overscroll Floating plug-in into the Plug-Ins folder.