Do I need to upgrade RAM if I upgrade a CPU?

[doggyworld]

If I upgrade my CPU and motherboard to an Athlon X2 250 which looks like it can support up to DDR2-800, but my current DDR2 ram is only DDR2-533, will this really hurt my performance if I don't upgrade my ram?

 

[ebaycj]

If I upgrade my CPU and motherboard to an Athlon X2 250 which looks like it can support up to DDR2-800, but my current DDR2 ram is only DDR2-533, will this really hurt my performance if I don't upgrade my ram?

It will likely work if the SPD on the memory correctly reports it as ddr2-533. It will not be as fast as if you had ddr2-800.