ddr400 compatibility with 533fsb

I currently have 512mb ddr333 ram and have hit my overclocking wall. I have 2 sticks of 512mb ddr400 lying around in my dads office.. On top of that it is corsair The only problem is that my processor (p4 2.8) has 533 fsb. The booklet says that it only supports up to ddr33. Conversely i have heard that if you knock down the speed in the bios for the ddr400 ram then it will work. This would be considered a free upgrade for me if it works. (double the capacity) Also i have my processor oc'ed to 3.3ghz. Would I stil be able to OC my machine if i put the ddr400 in (assuming its possible) From my point of view if i found a way to get it to work, it would have more headroom to oc. Am I wrong... its spec'd to run at 200mhz (400ddr) So logically i could now oc my processor to a 200mhz external clock (4.2ghz) assuming it didnt top out before then. I remeember trying this memory before (i had no clue what i was doing at the time) abd it didnt work. At that point i had the ram speed set to 400. Now i realize i need to scale that down... but to what. 266 or 333?

thanks a bunch... after major bios tweaking i got it to work.. Very Pleased