Memory compatibility with motherboard

[LuckyTaxi]

If a motherboard says its front-side bus is 333Mhz, does this mean I have to get memory that's also 333Mhz (PC2700)?

The CPU I plan on buying is a Sempron 2400

 

[AMDCrazy]

You can run slower memory like PC2100 but I wouldn't know why you would.