R51: Does it support DDR266?

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I've got a ThinkPad R51 (2887) with 256 MB of DDR333 RAM.

I got a 1 GB DDR266 RAM stick (they didn't have DDR333 and I didn't have time). Now, I can't boot with the 1 GB stick, in combination with the original RAM or standalone, and I'm wondering if I read the information wrong: I know that a higher speed, say DDR400, will run on a lower speed system, DDR333, just fine. It'll run at the lowest speed. But I assumed that a DDR266 will cause the existing DDR333 stick to run at DDR266 speeds. But as I think it over, it's probably not so.

So, does anyone have any suggestions on what to do? Apart from trying to get an exchange of course, that's a last resort. Any way to reduce the FSB or something to make it run the DDR266 stick? I don't mind the loss in speed, I just want to add the 1 GB stick or replace the 256 MB stick, either is fine.

[aaa]

I believe both sticks would go down to 266 without any settings being changed.