it really depends on your luck, however, as far as i know design wise*, it should last at up to 90 degrees celcius, mine did when i didn't have the heatsink on properly, however it throttled like hell and didn't get much work done and i don't know if it can sustain those temperatures without a shorter life span.
if thermal throttling/protection was disabled (which i don't know if you can do, i couldn't on my MoBo) and the heatsink is improperly installed, i think it wouldn't have any difficulty exceeding 90*C if your heatsink is properly on, it shouldn't be passing 70*C, even with bad ventilation
*Depends on which particular family of processors your talking about, i have a 630 prescott, i believe the northwood tolerations are about 15*c lower, my laptop shuts down at 75*c to prevent damage. use CPUz (google it) to find out which architecture you have
Ara