I am currently operating my Pentium Dual Core 2.66 GHz PC with a 256MB DDR2 RAM (400MHz)...I wanted to replace it with a 1GB DDR2 RAM..but it has 667MHz..can it be replaced?? or do I need a RAM with 400MHz to replace my existing RAM??

I am really clueless about the "MHz" thing..please forgive my ignorance..I just copied my RAM specifications from my PC manual..

Here are some additional details. I scanned my PC with Crucial System Scanner and got the following details:
# Maximum Memory Capacity: 4096MB
# Currently Installed Memory: 256MB
# Available Memory Slots: 3
# Total Memory Slots: 4
# Dual Channel Support: Yes
# CPU Manufacturer: GenuineIntel
# CPU Family: Intel(R) Pentium(R) D CPU 2.66GHz Model 4, Stepping 7
# CPU Speed: 2659 MHz

Each memory slot can hold DDR PC2700,DDR PC3200 with a maximum of 1GB per slot.*

*Not to exceed manufacturer supported memory.
So, shall I go ahead and purchase a DDR PC3200 RAM?? Wont it conflict with my present DDR2 RAM??