Actually KT266 can use either DDR or SDRAM, a lot of boards had only the DDR sockets onboard, but there were quite a few with both DDR and SDRAM sockets, 2 of each. So if you want a KT266 make sure it has SDRAM sockets.
The SiS735 chipset outperforms the KT266 however and is available on the K7S5A motherboard from ECS with 2DDR 2SDRAM sockets, but is unfortunately limited in overclocking options. However, for overclocking a duron it is okay, because pencilling in multipliers and voltages is easy on the duron and with an "overclocking BIOS" flashed to it a reasonable range of FSB values are available also. These boards can be got very cheaply.
regards,
Road Warrior