When your CPU and RAM FSB match it's on a 1:1 ratio which means they communicate at the same speed. This is the best setting for your computer for optimized speed.
Lets say you have a CPU whos (in your case since you have a 64) has a 200HTT in the BIOS, that 200 multiplied by the multiplier gives you your final clock speed and with 64's they also have an HTT multiplier, generally 4x or 5x depending on if it's a 1600"FSB" or 2000"FSB" CPU and board.
I put FSB in quotes because technically the 64's dont use the term FSB but simply HTT for the HyperTransport.
Anyway if your CPU is stock 200 (which it should be) but your RAM is say only PC2700 or 333FSB, then the RAM would need to be down at 166 and not 200 like the CPU.
Which means your RAM Ratio would be like 5:4 or something like that.
Know what I mean?
If your CPU and RAM are both at 200 and you want to OC your CPU while keeping a 1:1 ratio you are also OC'ing the RAM at that point.
BTW: Make sure your CPU is infact running at the speed it should be. A lot of people put a CPU in the motherboard and see it being recognized at a slower speed and it's because the mobo defaults the CPU down from 200 to like 100 in most cases and you need to set the appropriate HTT yourself.
So if you right click my computer>Properties and it's not being seen as a 1.8GHz 2800+ then you need to go into the BIOS and correct the settings