Hi Thunder,
Your memory is rated to do 400MHz (800DDR) speed maximum, but can also be used at the slower PC2-5400 speed (667DDR) or PC2-4200 speed (533DDR).
The SPD should have entries for all these 3 speeds, with the latency timings growing 'tighter' as speed decreases.
Y'see, the speed in MHz and the latency timing delay in clockcycles are inversely proportional - as the one increases the other decreases, and vice versa.
My SPD timings are:
266MHz - 3,4,4,10
333MHz - 4,5,5,13
400MHz - 5,5,5,15
Now, the theory is that if you were running your memory synchronous with your FSB 1:1 and were not overclocking, 3,4,4,10 timings would come up for the 266 FSB speed automatically.
Since you have your Conroe running @ 400MHz FSB 5,5,5,15 are correct timings for your memory at this speed (and should be delivered if memory set to 'Auto').
I would leave memory on Auto setting but, more importantly you must be aware the memory voltage must be set high enough - 1.8V is not enough.
Manually specify at least 2.0V if your mobo does not supply that on 'default' (which my ABit does).
Interestingly, I run a mild OC with my FSB @ 300MHz (1200QDR) which gives me 2.4GHz CPU.
My memory (set on Auto) comes up 4,4,4,10 at this speed which is between the registered values in the SPD - so it's perfect (and automatically perfect, even better LoL).
At the 400MHz maximum rated memory speed, you could attempt to run the memory timings listed in SPD for the next slower speed ie. DDR2-667 which would be 4,5,5,13 for my memory.
This is unlikely to work without at least 2.1~2.2V supplied to the memory, and very good system ventilation.
So you're good with the 'inversely proportional' thing now? It is a recurring concept that keeps popping up in science,
Regards