The stock heatsink/fan on a retail Celery700 is pretty pathetic, but does a reasonable job at stock speed. If you're looking for a quiet heatsink for overclocking, look at the Taisol CEKs and CGKs, can't beat them at that noise level.
As for hard disks, I've got two Fujitsu MPF3204AH's in my machine, and they are near-silent when operating - I can barely hear seeks with the fans in my machine OFF, let alone on. I've got two older IBM 22GXPs, and a newer 75GXP, and found that the noise of them "grows" slightly as they are worn in - not loud at all, but louder than my Fujitsus. They are 20gb, 7200rpm units, but AFAIK they are "only" UDMA66, which makes no appreciable difference in the slightest. Run cool to the touch even without ventilation (I've run them in my case with all the fans 'cept the CPU one disabled).
cheers
tweakr