Celeron Processor compatibility

I want to upgrade a 566MHZ processor in an HP Pavilion 6645C to a 1G processor. The part numbers are followed by a code that I believe is a reference to the chip or board architecture. The processors under 600MHZ use a code ‘PPPG while higher units show ‘FCPPG’. The latest Celeron processors show ‘Tualatin’ and I was able to determine that this is not compatible to the older board. I went to Intel’s website and did not find the answer. Can I make the upgrade with a processor that is ‘FCPPG’?