i think ddr2 uses higher timings because it runs at higher frequencies but i am not sure. ddr2 is still kinda new but you will get modules that have better timings by purchasing the low latency modules. check crucial, ocz, corsiar. i dont reccommend kingston because they tend to use more chips on their dimms which means you will most likely not be able to tweak anymore juice out of it. i think kingston uses a set of low class chips so i would never reccommend them.
also instead of spending all that cash on a conroe you could get better performance from a socket AM2 Athlon X2 which uses ddr2.
also a good cpu and ram is nothing without a good board so buy from ASUS or DFI and make sure it has dual channel support.