Unless your system is in a fairly hot climate, you should be fine with just a manufacturer-approved CPU fan and the standard fan in the power supply. Of course, multiple hard drives (especially SCSI ones) and multiple high-end video cards will drive up the heat.
Actually, I've done about a dozen Athlon XP 1700+ builds with only a standard AMD-approved AVC processor fan. No heat issues at all, and that chip runs warmer than yours does.
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