Hmm, please post your RAM, CPU (clockspeed, dual core or single or quad). Also post the settings you are using in dolphin, take a screenshot of the general tab and the general and advanced tab of the opengl plugin. My guess is your card is to weak, but I don't know and am going to look into it.
Edit: Yes it looks like your graphics card isn't good enough, simply purchasing a new graphics card should make dolphin work better, however, dolphin is a work in progress and if you don't have a really good cpu you wont see very good performance in game. My suggestion would be if you have a good system besides the gpu, simplly purchase a new one like a 8000 series nvidia or similar. This would be a cheap way to play all your wii and gamecube games. But if your CPU is under 2.5ghz dual core (this is not the minimum but a rough estimate of a cpu that will give you good speed) then you should go out and buy either a gamecube or a wii.
Edit: Yes it looks like your graphics card isn't good enough, simply purchasing a new graphics card should make dolphin work better, however, dolphin is a work in progress and if you don't have a really good cpu you wont see very good performance in game. My suggestion would be if you have a good system besides the gpu, simplly purchase a new one like a 8000 series nvidia or similar. This would be a cheap way to play all your wii and gamecube games. But if your CPU is under 2.5ghz dual core (this is not the minimum but a rough estimate of a cpu that will give you good speed) then you should go out and buy either a gamecube or a wii.