The reason why your games have a bad quality is mostly because of a poor computer configuration, that doesn't meet the minimum requirements for a smooth gameplay. Still, you can try to use a frame limiter, that can push down your game's number of frames per second. Dxtory has the ability to do that. Open the advanced tab, then check the "limit video fps" box and set your FPS. Go to http://dxtory.software.informer.com/ for more information. Also, on a single or dual core processor, an emulator determines your game to use 100% of its capabilities and slows down your computer. Make sure not to have too many active background processes.