DDR2 800 RAM is more than good enough if you plan to do little or no overclocking. If you get 1333FSb CPU then you will not be able to overclock the CPU with DDR2 667 RAM without also overclocking the RAM. The RAM must always run at least at the speed of the FSB (1333 FSB is actually 333MHzx4) and DDR2 RAM actually runs at 333MHz.
So if you plan to overclock the CPU a little, get DDR800 RAM and you won't ahve to overclock the RAM.