ExtremeTech has taken a look at SwiftShader 2.0, a software-based graphics solution that makes your processor render DirectX 9 and Shader Model 2.0 graphics.
SwiftShader 2.0 is unique among software rendering solutions in that it supports DirectX 9 (and DX8), and up to Shader Model 2.0. All graphics processing is handled entirely by the CPU. You just drop in a D3D8 or D3D9.DLL file into the directory of the application you want to run, and you're off. You can even download a free demo from TransGaming's site and try it out yourself. You obviously need some sort of interface to your monitor, so a graphics card or motherboard with integrated graphics are needed, but they'll essentially just sit there while your CPU does all the work. OpenGL is not supported, but TransGaming says a limited OpenGL-like API is under development.
Check it out over here. The reporter says the rendering solution is quite impressive but as you may expect the performance is nowhere near the performance achieved by a graphics card. A Intel Core 2 Quad 3GHz processor only managed to score 200 marks in 3DMark06 but the site says this technology may come in handy in the near-future to improve the base-level graphics of every PC.