1066MHz DDR2 unstable

I baught some OCZ Fatal1ty Edition memory rated at 1066 MHz (2.1v)

After installing it (motherboard supports up to 1066 without OC, 1600 OC'ed) the machine was just crap. I couldn't even start the XP installer. I "slowed" the memory to 800 by reducing the DRAM:FSB ratio and the PC running perfectly. After I finised installing everything I tried setting the BIOS back to "by SPD" settings and the machine was unusable again.

I also tried setting everything manually according to the ratings on the memory: 5-5-5-15 2.1v, but this didn't help either. I did some reading on various sites and apparently memory that is rated 1066 MHz at 2.1v is overclocked out of the factory as "normal" DDR2 memory runs at 1.8v.

Can anyone verify this, or perhaps give suggestions as to how to get the machine stable with memory running at 1066 MHz?

1600 is ddr3 memory.
there is no actual ddr2 1066 memory setting and requires overclocking of something. Your board may have compatibility issues with certain ram. This is quite common and your motherboard manufacturer will have a list of compatibe ram chips.
You take a risk when you buy 1066 ram.

evidently your board supports ddr3 ram as well though (although most of them only will accept two chips if they support both). If you can't return the ram you're hosed. if you can, buy some 1600. It's much, much faster than ddr2 and uses less electricity.

finally, both intel and amd have some processors that you can fry the memory controller if you run it over 1.8 volts for an extended amount of time, and have warnings.