Yes, the X800 does support this.
I get those graphical glitches sometimes with my ati card and still I don't know exactly what it causes.
Have you tried to disable vsync again? Basicaliy what vsync does is force the videooutput to syncronize with the monitor,
so the game seems to be smother.

You can try looking through your ati control panel or control center and look after some compatibility options.
You can check or uncheck some and try and error it. Good luck.

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