The really tricky part of glass effects is that you need triple-buffering. Making a glass "window" that is completely inside another of your windows (like buttons on a toolbar, or a webpage) is quite easy, if you're good enough at graphics programming. To make a real window glassy, and interact with the other windows would be really tough... you need to capture an image of what's underneath the window, blur it, then apply other effects. But capturing what's beneath a window is very difficult without hiding the top window, which makes it flicker (like the "transparency" effects for pre-2k windows, they were all slow or flickery).
If you don't need a perfect glass effect, just an "ok" one, then there's an example on psc:
I've not had much (any) experience with visualstyles, and I don't use bb, so for that I'm not sure.
On the other hand, I'm pretty certain that adapting code from a skin app like CustomEyes or ShellVM could do it. You just have to trap the WM_NCPAINT message (and a few other ones) for every window in the system and paint for them. While the codebase for ShellVM (there might be better apps about now, I haven't done this for a while) is quite large and difficult to get to grips with, basic window invasion techniques can be learnt from iconizer (C), and window skinning techniques from the tutorial at VB Accelerator (VB6). Combining the two, as well as the previous example as PSC should get you what you want.
It sounds like quite a challenge, actually. If only I had the time...