Can i have one 667 and one 800 MHz DDR2 RAMs on my system?

I have a ASUS P2NPV-VM (basically a nVidia 430/6150 chipset) and already have a Transcend (the only good brand available in India) 1 GB 667MHz DDR2 RAM.... Was thinking of adding another Transcend 1GB but 800 MHz RAM... So will my machine work "perfectly"? At what speed will the RAMs work?