Check on Intel's web site and find out the power dissipation for it (Watts). If it is much more than 10 or 15W , passive cooling is unlikely. If it's on a socket 370 mobo that supports it (possibly needing a BIOS update), and you're willing to lose some performance, it could be replaced with a VIA C3 (1GHz or so) which is capable of being passively cooled.
.bh.