TweakWindow

Do you admire the transparent windows of Windows Vista and the upcoming Windows 7, but crave the familiarity of XP? No problem. TweakWindow gives you the best of both worlds: You get to keep Windows XP and enjoy transparent windows too. And not only can this program make window borders transparent, as Vista and Windows 7 do, but it can also make each entire window transparent. On top of that, you can control exactly how transparent the windows are, starting with no transparency and moving all the way up to absolute invisibility. Better still, you can customize the transparency of individual program windows, making some more transparent than others.

Another option is to turn some windows into "ghost" windows that are transparent and allow you to click through them to windows beneath. You can also minimize an entire window into a floating toolbar with the program's "rollup" feature. And you can even make the Windows taskbar transparent.

--Preston Gralla