change your video card, 4gb of ram, win7 64bit, and overclock your cpu..

 

1.- Overclock your CPU, if your PC is custom builded, then is almost sure the Mobo's BIOS have a FSB controller, and even if you cannot touch voltages that CPU will hit near 3GHz with everything at stock.

2.- Your RAM is fine, 2GB more than enough for the emu.

3.- UPGRADE your OS to a 64 bit one, Dolphin in most cases gets a huge boost using the 64-bit version.

4.- Your VGA is weak and It may be the culprit of the low FPS, use native resolution with zero AA and AF, but I strongly recommend an upgrade, with a 9800GT you're ready to go with almost all games.

 

do what ARC@NO says but....
... if you planned to spend money on a uptade only for dolphin... buy a Wii.