There are no CPU updates from AMD. Any updates to the CPU would probably in the kernel of windows XP. This means that it has to do with Microsoft with regards to the kernel. Basically windows updates.
However, I highly doubt this is your issue. With regards to you AMD system, keep in mind AMD only makes your CPU, not the computer. So any updates to your system would come from either your computer manufacturer ( HP, Compaq, ...etc.) or from the manufacturer of the component. Most performance issues have to do with the motherboard drivers and video card drivers. So see what kind of motherboard you have and video card and get the driver from the respective manufacturers.
With regards to the comments about the CPU 698MHz, this is common. This has do do with tolerances in chips and other electronic devices. 2 MHz is nothing at all. Usually not the CPU but the motherboard that controls the clock frequency. I bet if it was on an Asus motherboard it would run a little above 700MHz.
Any ways hope this helps.