Well, nVidia puts out proprietary drivers for their chipset, and ATI puts out proprietary drivers for their graphics cards. As for myself, if everything was working I would just stick with the stock open-source drivers.
Noting that you have a Radeon X300, I'm guessing top-notch gaming performance isn't your top priority, so I would think the stock "radeon" driver is probably sufficient.
I also don't know about compatibility between the nVidia proprietary chipset drivers and the ATI proprietary graphics drivers.
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