You didn't make yourself very clear. What exactly do you mean by "Some programs use more than 100% processortime."? Do you mean that some programs use 100% of the processor all the time? And if you do then it could be a virus, or it could just be the program which requires a lot of processor power. What program is it? You can check your processor usage and programs by press Ctrl+Alt+Delete in Windows XP, and looking at the numbers next to the programs and the box that says "CPU Usage".
Hope that helped.