There are just two different naming schemes when it comes to DDR. The first you mentioned, DDR 266, is reporting the speed which runs at 266MHz. For this type of memory, you could also report the bandwidth instead, which is rougly 2.1GB/s (or 2100MB/s). Therefore, they also refer to it as PC2100.
Others:
DDR 200 = PC1600
DDR 266 = PC2100
DDR 333 = PC2700
DDR 400 = PC3200
...
~cdogg
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