If memory serves me correctly, the 6200 is roughly equivalent to the Radeon 9600, (the PCI-e version is known as the X300) or at best, the 9600pro. (X600pro) The Radeon 9800XT, SM 3.0 support aside, should even hold a slight edge over the GeForce 6600GT, thanks to some other features, most notably its 256-bit memory interface, which makes its RAM bandwidth double that of an equivalent-speed (MHz) RAM on a mid-range to entry-level card like the 6600 and 6200 cards.
If there isn't some other concern at work here, (namely, price) get the 9800XT hands-down. It may be considered a little "outdated" as it's from the 2003 generation, but it definitely holds its own in today's world, and can comfortably run any game out there with most to all of the detail settings turned up.