From a previous post you made, I'm assuming you have an AM2 AMD Sempron 2800+ or 3000+ 1.6GHz. However, there are two versions, a 35W one which has a maximum temperature of 78C, so if you have that version you should keep your temperature below 70C approximately. If you have the Sempron 2800+ or the 62W version of the 3000+, the maximum temperature is between 55C - 69C, so you should keep your processor temperature at around 50C maximum.