What is the RAM speeed you have to select for a P-4 processor?

Processor Type is not important when selecting memory. It's the FSB (Front Side Bus) speed that's important... FSB400 PC3200 FSB333 PC2700 FSB266 PC2100 If you have a processor with a 400MHz FSB, then you need a Motherboard which supports a 400MHz FSB. You then select the appropriate memory.