CPU Heat

I have a Celeron 566mhz in my machine, which is now just over a year old. I have noticed that my machine is now often exceeding 40 degrees celcius. I was wondering exactly how hot is too hot. I currently use my temperature and power management features of my BIOS to automatically kill my system if the temperature exceeds 60 degrees celcius. What is a safe operating temperature and should I now be looking for a new CPU to replace my current one since simply replacing the Fan would be impractical?