Depends on your CPU FSB
If you use a 400 MHz FSB CPU and want to overclock, then get DDR433 (aka PC3500)
If you use a 400 MHz FSB CPU and don't want to overclock, then get DDR400 (aka PC3200)
If you use a 266/333 MHz FSB CPU and want to overclock, then get DDR400 or DDR433
If you use a 266/333 MHz FSB CPU and don't want to overclock, then get DDR333 (aka PC2700)
And get CL2.0 RAM instead of CL2.5 or CL3.0 for best performance. (Kingston HyperX and Corsair XMS for example)
----------------
<b><A HREF="http://geocities.com/spitfire_x86" target="_new">My Website</A></b>
<b><A HREF="http://geocities.com/spitfire_x86/myrig.html" target="_new">My Rig & 3DMark score</A></b>