pcsx2 needs a good pc to run at full speed
Most of the slowdown if because the specs you have, you will need at least 3 Ghz clocked dual processor, pcxs2 only uses dual processor so higher numbers of cores doesn't help the emulation, only higher clock rates does, I have mine clocked at 4Ghz and all games runs full speed, at east what I have tried.
Even video cards are no as decisive as processor for PSX2 emulation; you both lack of video power, I think you will need at least an Ati Radeon HD 3000 series or Nvidia GeForce 6600, of course higher is better, but after Radeon HD 4850 or GeForfe GTX 280; you won't find any speed improvement, after that you will need pure main processor brute force.
----------------------------------------------------
Windows 7 Professional x64 // Arch Linux x64
AMD Phenom II x6 1090T clocked at 4000 Mhz
8 Gb Dual Ram Corsair, running at 2000 Mhz
Ati Radeon HD 4850 1 Gb Ram
Mother Board Asus M4A89TD PRO/USB3