Problems with alpha-blur in Compiz Fusion

I have an ATI Radeon Xpress 200M video card, or something along those lines, and am using the restricted drivers under XGL in Ubuntu Gutsy Gibbon 7.10.  Most everything in Compiz Fusion works nicely and smoothly except for the alpha-blur.  Alpha-blur is when transparent objects blur the content behind them, sort of like in Vista window-borders, or behind "sheets" in Leopard, I think. Anyway, I have been trying to get it to work for ages, but whenever I get close, my computer starts to freeze up and it takes a few minutes before I can revert to the old settings.  An important thing to note is that the blur did work smoothly in the old Beryl, but it doesn't work in Compiz Fusion.  What has changed that makes it not work?  It is really quite annoying to me.

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