Funny... with the RENDER option in Mandriva Control Center disabled it lags as much or little more than with it enabled.
Actually it seems, that Mandriva Control Center doesn't enable RENDER in xorg.conf, but some option called RenderAccel. The label says Enable RENDER Acceleration. I had just expected it to enable RENDER, but guess I was wrong :P
RenderAccel is specifically for the nvidia driver... In recent drivers its enabled by default. In recent Xorg RENDER is also enabled by default...in theory you shouldn't need to have it enabled specifically, however I don't really know how mandriva does things
I'm seeing the exact same problems on my laptop with a 8400GS card. Read somewhere, might have been on this forum, but I can't remember) that there is a problem with 8xxx cards and compiz. Especially cube and blur.
I have just tried 173.08 and the problem is still there.