Arrrgh!¬
Exactly the same problem on a new build I'm doing right now…
Sitting there watching the temps -
Stable at 48 deg C CPU temp for 15 minutes, then shuts down with an overheat warning.
It's completely bizarre!

This happened to my SN41G2, all I did to solve the problem was re-seat the cpu and apply a very small amount of compund. . . .

Specs:

2800XP+
2x512MB PC3200
DVD-ROM
120GB Hard Disk

I'll try that - have already reapplied thermal compound - just a tiny bit… will try re-seating the heat-pipe

did you remove the plastic film off the shim?

have you got the FSB jumper set correctly?

*grin* - yes… replaced the fan with a nice little coolermaster unit - reseated the ICE and reapplied thermal paste.
Unknown which worked - but is now 60% quieter ( thinking maybe the fan was duff)
… actually - could well be, as it was shutting down at 48 deg. C, which is when the fan speed was supposed to increase.

Very odd tho.

Cheers anyway! ;)