my AMD athlon 1ghz is running at 1025mhz instead of 1000mhz why is it running at a higher speed
Reason 1: Because electronics are precision devices that have slight tolerance ranges within which they can operate. There is a technology known as Spread Spectrum that allows the exact clock speed to vary and deviate slightly (within a very small range) in order to reduce EMI.
Reason 2: Many motherboards, especially those with AWARD Bios, have a "turbo mode" feature. This is a feature which gives a very slight increase to FSB, usually in the range of 2-3mhz, to get you a "slight" performance boost. It is rarely if ever harmful and is typically disabled by default. However, if it is enabled on yours, the FSB of your motherboard may actually be higher.
Reason 3: Imprecise clockspeed detection algorithim being used to detect CPU speed. With a device that is fluctuating so incredibly fast, it can be very difficult to register the *exact* clock speed of a processor. Though it may be running at, say, 1004mhz, different algorithims will give different readings based not only on the program being used, but also the load on the processor at a time. Try it. Get a cpu-speed detection program and run it while at 0% load. You may get a reading of 1017mhz. Run it again when your CPU is at 100% and your system is under load. You may get readings that are completely wrong.
Your front side bus is CLOSE to 133.33333333333333mhz, but may be closer to 136mhz than 133. The clock attempts to achieve 133mhz, but will deviate slightly, for either reasons 1, 2 or 3, or a combination thereof, and is giving you the aforementioned clock speed.