I feel like what I post just gets ignored sometimes. "You can't emulate PSP games [edit]yet[/edit]. There's no emulator that plays commercial games available for them on the PC."
That went ova' your head - Demo's are games, Shorter simpler versions.
Minimal Specs:
AMD XP/64 or Intel Pentium 4 (VM Built will not work with non SSE2 CPU's)
512MB of RAM
Pixel Shader 1.4 supporting card (GSdx Graphics Plugin Only)
Recommended Specs: (For reasonable preformance in many games, but not all)
AMD64 X2 or Intel Conroe E6600+ (Multi Threading is supported in PCSX2)
512-1024MB of RAM (more RAM allows for VM mode to be stable)
Pixel Shader 2.0 supporting card (recommended GeForce 6600-8800 or equivilent ATi card)
Hope that helps spec's wise for the PS2 emulation!
Still, You never really know how the emulator will perform unless you try it for yourself. With the right plugins, Tweaks and settings people have gotten it to run on sub-Ghz processors and Radeon 9200's