For the most part Windows XP is always setup by the manufacturers for the least power consumption. Your computer will always throttle down, in certain areas, in order to use the least power as long as its setup in the Power Scheme section of the Power Options. I've noticed it in all forms of processors that have the throttle back features. The easiest thing to do is to go into the Power Scheme Settings (right click on desktop, select Display Properties, Screen Saver - Power... where it says monitor power). In there you will get a power scheme with 2 lists, one stating that while the laptop is plugged in and one while its running from the battery. Usually the plugged in setup is set for Portable\Laptop.
Change this to Home\Office Desk. When this is applied the computer will (should) run at the its full power and highest settings. There is always a chance that the laptop may come with Manufacturer based software which will conflict with the XP based settings. You can leave the Battery section alone and it should throttle back power and settings when you disconnect the power supply. As for the AMD fix, i have not noticed a problem with either Intel or AMD procs running at full speed once the limitations are removed. Just run dxdiag to get a report of the processors speed. It may not be the best way, but its an easy way as it will state the proc's speed and its actual current speed its running at.