The registry tweak does not work on the RTM build, it used to work in around build 5308.
You can still get the transparency effect on Vista and XP by using WindowBlinds, not the shareware version but the paid version, and using Aero skins created by users like Jemaho or WindowsX. But keep in mind that even WindowBlinds has a requirement for the transparency effect, abeit much lower than vista's requirement.
WindowBlinds works well on Intel 915, whereas Vista's Aero does not.