Actual Transparent Windows lets you apply a transparency effect to any window in Windows 2000/XP. The transparency effect looks very impressive and may be useful with such objects as Windows Taskbar, WinAmp, drop-down menus and other windows.
Actual Transparent Windows lets you set individual transparency rate for each window. You can change transparency from 0% (fully transparent) to 100% (solid) to achieve the desired effect.
More info:
hxxp://www.actualtools.com/transparentwindows/index.shtml