yea... you said you installed the AMD proccessor drivers. the AMD proccessor actually doesnt need any, its typically used for "Cool & Quiet" as mentioned above.
witch would explain the Core Speed fluctuation... that means Cool & Quiet is doing its job.
watch, try this.... download both... SuperPI http://www.xtremesystems.com/pi/index.php
,and Prime95 http://www.mersenne.org/freesoft.htm
because your CPU is Dual core you may need to run 2 programs at once to put it under full load... SuperPI just puts a large load on the CPU while it calulates the #pi, put it at a high option and it takes longer... And you can run Prime95's toruture test at the same time, just stick it on "max heat".
once both those programs start up, your Core speed will probably jump strait to 2000mhz. try it if you like. at least youl now its working proplery.
also if you wonted to disable Cool and Quit, there may be a option in your BIOS... if not there may be an option in /control pannel/power options/Power scheme..... the power scheme iv heard can change Cool & quite settings. (I dont know what the setting is htough i dont have Q&C)
and or unintall the proccessor driver.... heres the exact quote from AMD's proccessor driver description.... "AMD Athlon¬ô 64 X2 Dual Core Processor Driver for Windows XP and Windows Server 2003 Version (exe) 1.2.2 - Allows the system to automatically adjust the CPU speed, voltage and power combination that match the instantaneous user performance need."
EDIT: yea i found the exact instructions about changing the optinons the the controle pannel/power
just go to Page 9 on this PDF.... http://www.amd.com/us-en/assets/cont...ion_Guide3.pdf