Sorry, I was a little late posting this :)
Glass2k allows Windows 2000/XP users to make any/every window transparent/semi-transparent, like Linux or Mac OS X windows. The latest version remembers each window's transparency settings, allows you to keep any window on top, loads on Windows startup, beeps when glassify'ng a window, supports mouse and keyboard shortcuts, and allows you to customize these shortcuts.
Download: Glass2k - Beta Version 0.9.2 : 54 kb.
This is BETA software!, please use caution when installing it on your system
News source: Glass2k Website