Strange Performance and Possibly Modded Drivers?

[AnyOldName3]

As dolphin's got more accurate, it's had to drop support for hardware and software configurations which don't allow more accurate code to be used. FOr example DirectX9's D3D module didn't support integer maths, which is what the GC and Wii's GPUs use, so we had to drop support for DirectX 9, in favor of OpenGL and DirectX 11.

As for your GPU, it's missing features such as a compatible version of Pixel Shader, so you'll only be able to use revisions of Dolphin from before the change to whatever version we use now. This is missing at a hardware level, and it would be far more work than earning the money for a new computer to modify your graphics drivers to emulate it.