800MHz FSB means 200MHz FSB x 4, as Intel CPU's are "quad-pumped".
And 200MHz FSB applies to both, CPU and RAM.
200MHz FSB x 10/6 Memory Multiplier = 333MHz memory bus x 2 DDR = 667 MHz memory speed.
So 800 and 667 is achieved using 200MHz "base" FSB speed.
You can have problems with 667MHz memory and FSB speeds exceeding 333MHz FSB, as 333 x 2 for memory bus would be 667.