Crystal XP is an application that enhances the trasparency of your desktop and open windows as its basic design. With the add-ons it enhances video graphics for your icons plus has different skins to dress up your desktop. The whole thing is kind of open source like with its following. The forums contain great tutorials on its usage and help on building graphical window enhancements.

This is kind of techie in understanding and using the applications> there are other out there that are much easier to use: such as windowblinds.

Stardock WindowBlinds