One of the most important requirements for PlaneShift is a full featured OpenGL driver.
The fact that such heavy games like "Sims 2" run properly shows that you may have a good 3D GPU. Some of such games, which are often made for Windows only, may use the Direct3D interface and be happy that DirectX is installed.
But PlaneShift is a cross-platform game, it shall work under Windows, Linux, and MacOS. DirectX is not available under Linux and MacOS, of course. So PlaneShift needs to use a cross-platform 3D interface -- OpenGL.
Unfortunately, Windows ships only drivers which do not yet support OpenGL completely, including 3D accelleration. You will have to get current drivers for your specific on-board controller, most probably from the website of your mainboard manufacturer.
Try to find out which graphic chip (GPU) you have exactly. A tool like "Everest" may help you, if the system and driver details don't tell you enough (see the Device Manager).