Firstly, windows XP and 2003 server dont report the correct speeds and so it will almost allways say 800mhz in the system properties.
now that thats said, I had the same problems and I solved them by uninstalling all the AMD drivers and utilities. I then did the hackflag fix which involves adding the following entry into the registry.
I then reinstalled the AMD drivers and after that went to device manager and processors and clicked update driver. This then found the driver as AMDK8 and changed the driver file from processr.sys to AMDK8.sys
It seems that AMD have updated the driver to K8 and not told microsoft!!
I then reinstalled the AMDCLOCK and dashboard softwarehttp://www.amd.com/us-en/Processors/..._12474,00.html
now everything appears to work. the amdclock changes dependant on the load and if i change power to alway on it jumps to 1600mhz
hope that help someone