If you really mean Aero Glass , then I think you're out of luck. The hardware acceleration required to create this effect is only supported by Vista DWM (Desktop Window Manager), which works by arranging multiple windows together in one processed layer.
If you just want transparency and non-rectangular windows, this can certainly be achieved in XP, as evidenced by the fact that Windows Live Messenger can do this. See Layered Windows on MSDN.
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