RAM compatability. I have a Sony VAIO and want to upgrade my RAM a second time. I've already

Question

I have a Sony VAIO and want to upgrade my RAM a second time. I've already upgraded once and the disc I installed then is a DDR PC2-5300. This time around I consulted Sony.com, which advises that I install a DDR2 PC-3200 400 MHz disc. My question is, does it matter that one disc is a DDR PC2-5300 and the other will be a DDR2 PC-3200? Are they compatible? What is the difference between these two types of disc?