Dolphin and many other Gamecube emulators are far from perfect in they´re actual releases.... so you can´t expect to play the game at full speed or even near. probably in the future but you will need a fast PC for that.
at the moment as i sayd in my last post... i recommend you to play the game on a Gamecube! there i can promise you to get full speed and no graphic glitches

for a lower price.
to my knowledges this is the PC you need to emulate the Gamecube at full speed.
- Intel core 2 duo or AMD X2 with at least 1800mhz(i think single Overclocked opterons with a nice E6 stepping and a good cooling fan can do the job aswell)
- 1024 of DDR Ram
- a good mainboard
- at least a Ati X1XXX or a Geforce 7XXX with 256 MB
and many other things we don´t need to mention now.
all those components are about 600-900 Euros
last but not least a emulator in a very advanced stage.
a simple Gamecube can be found between 40-130 Euros
with the components you need to emulate the gamecube you can buy at least 5 Gamecubes!
and if you want to play them on your PC i recommend you to wait untill we can see some progress of the actual emulators or just use a TVcard and DScaler!
easy... isn´t???
Greetz
@ruantec-Man