From www.silentpcreview.com:
Intel P4 Willamette core (1.3-2.0 GHz):
Early P4s with typical power from 49W to 75W, these hot processors are difficult to cool quietly, despite the large HS form factor. Serious undervolting and underclocking may work. Thermal protection throttles speed under high loads so maximum power (100W for 2GHz) may never be reached. Thus, these (and all P4s) very tolerant of thermal abuse.
IMHO, if your CPU is idling under 50ºC and stays under 70ºC at load, you should be OK. Cooler is always better of course -- CPU temps of mid-30s at idle and under 50ºC at load are what most users should aim for.