What happens if I use DDR2 PC2 5300 667 MHZ for a PC that uses DDR memory at a lower speed?

I have 2 dimms (2gb) of DDR2 PC2 5300 667 MHZ memory and would like to know if I can insert them into my Dell Dimension 3000 desktop. This is what crucial says about my PC's ram compatibility - http://www.crucial.com/store/listparts.aspx?model=Dimension%203000&Cat=RAM - , but I wasn't sure if DDR2 was backwards compatible with older ram.