If you want speed like playing it on the Gamecube or Wii, it just isn't going to happen right now. There are some games that exhibit slowdowns or random unexplained lag on even the beastliest of machines with the most powerful hardware.
The first thing is, you are going to need a more powerful processor. Amd processors just are not efficient for CPU intensive emulators such as Pcsx2 and Dolphin, especially last generation Amd processors like the Athlon64 and Athlon 64 x 2.
There is probably some games that will run with decent speed or close to full speed, but most games will typically run at around half speed with that processor.
Generally a decent dual core processor such as a Core2Duo should be sufficient, only higher end models such as the E6xxx, E7xxx, and E8xxx models. I am unsure how an AMD Phenom fares in Dolphin, it seems that Intel's offerings seem to be more recommended and preferred for emulators such as Pcsx2 and Dolphin. Quad core is really pointless since Dolphin is not optimized or coded for Quad core processors nor will it ever be since there is little to no performance benefit to be had.
Your video card is sufficient enough for Dolphin, but may not be able to handle all the bells and whistles such as AA and AF.
The plugins that come with Dolphin, are the only plugins available. All that I can suggest is keep trying the latest revisions or upgrade your hardware to something more powerful.
1.5 GB of ram should be enough, but it never hurts to have more ram for applications and overhead.
