WindowBlinds

  WindowBlinds is the world's most popular desktop enhancement utility. With a user base estimated at around 10 million, WindowBlinds is used by both consumers and corporations who want to change the way the Windows user interface looks and feels. It is the only program of its kind used and certified by Microsoft.

WindowBlinds 4.5 includes the new ability to change the color of visual styles through hue shifting along with modifying the brightness and saturation of the visual style. It also includes the ability to have alpha blended Start menus and standard menus which enable users to have semi-transparent pieces to those parts of Windows XP and eliminates the "jagged" look around the edges of the interface. WindowBlinds 4.51 enables users to have semitransparent pieces in the Start menu, adds support for 64-bit version of Windows XP and enhanced support for instant messenger clients.

Consumers can purchase the enhanced version of WindowBlinds for $19.95 which adds the ability to skin more elements of the Windows user interface and can skin even non-theme aware applications.

See http://www.stardock.com/products/directskin/ for information on how you can make your own application skinnable.