The linked hotfix drivers refer specifically to the following:
"No compatible hardware found" error message appears when using the AMD Catalyst drivers provided on the AMD Graphics Drivers & Software page or "a conflict between Microsoft DirectX® and the AMD Radeon™ HD AGP series graphics cards."
Which, according to your post, is not the problem you're experiencing. I'd suggest installing Sysinternals Process Explorer v15.3
and then observe it while it monitors (in real time) which process is actually causing the spike in CPU usage. This would allow you to see whether there's a DirectX conflict causing the spike, or some other process entirely.
For your consideration; my experience upgrading PCs for clients choosing to use their older AMD/ATI chipset based AGP cards, has been that unless the card was actually manufactured and released by AMD, the AMD drivers are likely to either fail to install, or install with errors. As a recent example; I installed Windows 7 for a client who wanted to use his old Diamond AGP card based on the Radeon 9250 chipset. None of AMD's drivers for the 9250 (let alone Catalyst) would install correctly on that card. After doing some searching; the driver downloaded from Diamond installed and functioned perfectly.