The AMD761 is a good chipset (except for the normal problems with the Via686b Southbridge). It can be found on the Asus A7M266, among others.
DDR will offer a decent performance difference over SDRAM. However, if you are willing to wait, you might want to look at the nForce, when it comes out. It has dual-channel SDRAM and DDR support, and both can be used at once.
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