I had it on for about 1 hour compiling X11 for Linux so it was working fairly hard. Always been a bit suspicioius of how often the fan came on but then it is a Celeron 2.5gHz - not known for having a low running temp.
Just tried turning it on again having left it for about 45 mins but the same thing happens.
I think may be the CPU has burned out, but normally the fan will crank up a few notches if it starts to get really hot but it didn't do this.
Ahh, just got wireless working really well in Linux as well.